Introduction: Why Underlining in PDFs Matters
Ever wished you could mark up a PDF as easily as a physical book? Whether you’re studying for exams, reviewing contracts, or analyzing reports, underlining important sections helps you retain information, highlight key points, and stay organized.
Unlike printed documents, where a simple pen or highlighter does the trick, PDFs require digital tools to add underlines. Luckily, modern PDF editors make this process easy, whether you’re on a computer, tablet, or smartphone.
Why Underlining in PDFs is Useful
✅ Enhances comprehension – Helps you focus on key ideas while reading.
✅ Improves document review – Makes it easier to refer back to important sections.
✅ Great for collaboration – Allows teams to highlight crucial parts of reports or agreements.
What You’ll Learn in This Guide
- Different ways to underline text in a PDF (using built-in tools and online editors).
- Step-by-step instructions for popular PDF software like Adobe Acrobat, PDF4Sure, and free online tools.
- Pro tips for effective document markup to boost productivity.
By the end of this article, you’ll know exactly how to underline text in a PDF like a pro—no printing required!
Can You Underline Text in a PDF?
Many people assume that PDFs are fixed, uneditable documents, but that’s far from the truth! While PDFs are designed to maintain formatting across devices, they can be annotated, highlighted, and even edited—you just need the right tools.
Yes, You Can Underline in a PDF! Here’s How:
There are two main ways to underline text in a PDF, depending on whether you’re simply marking up the document or editing the actual text.
1. Using Annotation Tools (Most Common Method)
Most PDF readers and editors come with built-in annotation tools that let you underline text without altering the document’s content. This method is perfect for reading, studying, and reviewing.
- Adobe Acrobat Reader → Use the Comment tool to add underlines.
- PDF4Sure → Select the Underline tool in the annotation menu.
- Foxit Reader, Preview (Mac), or online PDF editors → Similar underline features available.
✅ Pros: Simple, quick, doesn’t change the original text.
❌ Cons: Annotations are separate from the text, so they won’t transfer if copied elsewhere.
2. Editing the Actual Text (Advanced Method)
If you need to underline text within the document itself (as part of formatting), you’ll need an advanced PDF editor that allows direct text editing.
- Adobe Acrobat Pro → Convert the PDF to an editable format, then underline text.
- Online PDF editors → Some allow text formatting changes.
✅ Pros: Permanent underlining, useful for document creation.
❌ Cons: Requires an editable PDF (won’t work on scanned documents).
Yes, you can underline text in a PDF! Whether you need a temporary markup or a permanent edit, there’s a method that fits your needs.
How to Underline Text in a PDF: Step-by-Step Guide
Underlining text in a PDF is an essential feature for students, professionals, and anyone who needs to highlight important information. Whether you’re reviewing a legal contract, studying an academic paper, or marking key points in a report, underlining helps you stay organized and improve readability. Since PDFs are fixed-format documents, editing them directly isn’t always straightforward—but with the right tools, you can easily add underlines.
Below, we’ll cover three different methods to underline text in a PDF: using Adobe Acrobat Reader (free), Adobe Acrobat Pro (paid), and browser-based PDF viewers like Chrome and Edge. Each method serves different needs, so choose the one that best suits your workflow.
Using Adobe Acrobat Reader (Free Version)
Adobe Acrobat Reader is one of the most widely used PDF viewers, and its free version allows you to underline text using annotation tools. This method does not modify the actual text but adds a visual underline to help highlight key parts of the document.
Step 1: Open Your PDF in Adobe Acrobat Reader
If you don’t already have Adobe Acrobat Reader installed, you can download it for free from the Adobe website. Once installed:
1. Launch Adobe Acrobat Reader.
2. Click File > Open and select the PDF you want to annotate.
Step 2: Select the “Comment” Tool
1. At the top of the window, click on the “Tools” tab.
2. Scroll down and select “Comment”—this opens the annotation toolbar.
3. Alternatively, you can press Ctrl + Shift + 8 to open the commenting tools directly.
Step 3: Underline Text Using the Annotation Tool
1. In the toolbar, find the underline tool (marked by a “T” with an underline).
2. Click the tool and then drag your cursor over the text you want to underline.
3. The selected text will now have a colored underline.
Step 4: Customize Your Underline *(Optional)*
- Right-click on the underline and choose “Properties” to change the color, thickness, or opacity.
- You can also add a note explaining why you underlined a particular section.
Step 5: Save the Changes
1. Click File > Save or press Ctrl + S to ensure your underlines are preserved.
2. The annotated PDF is now ready to be shared or printed.
✅ Best For: Quick markups, studying, reviewing documents.
❌ Limitations: The underline is an annotation, not part of the actual text.
Using Adobe Acrobat Pro (Paid Version)
If you need to underline actual text within the document (not just as an annotation), you’ll need Adobe Acrobat Pro. This method allows you to permanently edit the PDF’s text, making it ideal for creating professional documents.
Step 1: Open the PDF in Adobe Acrobat Pro
1. Launch Adobe Acrobat Pro (available via subscription).
2. Click File > Open and select your PDF.
Step 2: Use the “Edit PDF” Tool
1. In the right-hand panel, select “Edit PDF”.
2. The document’s text will now become editable, allowing direct modifications.
Step 3: Underline the Text
1. Highlight the text you want to underline.
2. Click the “U” (underline) button in the text formatting toolbar.
3. The underline will be applied permanently, making it part of the document’s text.
Step 4: Save and Export Your Updated File
1. Click File > Save As and choose a new file name if you want to keep a copy of the original.
2. Your changes will now be part of the PDF itself, rather than just annotations.
✅ Best For: Editing official documents, creating PDFs with permanent formatting.
❌ Limitations: Requires a paid Adobe Acrobat Pro subscription.
Using Browser-Based PDF Viewers (Chrome & Edge)
If you don’t want to install additional software, Google Chrome and Microsoft Edge offer built-in annotation tools that let you underline text in a PDF. While these tools don’t allow permanent text editing, they are great for quick markups.
Step 1: Open the PDF in Your Browser
1. Right-click on the PDF file and select “Open with” > Chrome (or Edge).
2. The PDF will open in the browser’s built-in viewer.
Step 2: Use the Annotation Tool
1. In Microsoft Edge:
Click on the pen icon in the top-right corner.
Select the underline tool and drag your cursor over the text.
2. In Google Chrome:
Chrome doesn’t have a built-in annotation tool for PDFs, but you can use a browser extension like Kami or Lumin PDF.
Step 3: Save the Modified Document
1. Click the Save or Download button to store your underlined PDF.
2. If using Edge, your annotations will be saved automatically.
✅ Best For: Quick annotations without extra software.
❌ Limitations: Limited functionality, may not work on all PDFs.
Each of these methods allows you to underline text in a PDF, but your choice depends on your needs. If you just want temporary markups, go with Adobe Acrobat Reader or a browser-based tool. However, if you need permanent text formatting, an advanced PDF editor like Adobe Acrobat Pro is the best solution.
Free Online Tools for Underlining PDFs
If you need to underline text in a PDF but don’t want to install any software, online PDF editors offer a fast and convenient solution. These web-based tools allow you to add annotations, underline important text, and save changes without requiring downloads or subscriptions. Below are some of the best free online tools for underlining PDFs, each with its own unique features.
1. PDF4Sure – Quick, Easy, and Free PDF Annotation
PDF4Sure is a user-friendly online PDF editor designed for quick document markups. It allows users to underline, highlight, and annotate PDFs effortlessly. The tool is completely free to use and doesn’t require any software installation.
How to Underline a PDF Using PDF4Sure
1. Go to the PDF4Sure website (accessible from any browser).
2. Click “Upload PDF” and select the file you want to edit.
3. Once the PDF loads, select the Underline Tool from the annotation menu.
4. Click and drag your cursor over the text to apply the underline.
5. If needed, customize the underline color and thickness.
6. Click “Download” to save your edited PDF.
✅ Pros:
✔ Completely free with no hidden charges.
✔ Simple interface, ideal for beginners.
✔ Works on all devices (PC, Mac, tablets).
❌ Cons:
✘ Requires an internet connection.
✘ Limited to basic editing features (no text modifications).
2. Smallpdf – Simple Web-Based Underlining Tool
Smallpdf is a well-known PDF editor that provides a range of tools, including the ability to underline and highlight text. It is a great option if you’re looking for fast, no-hassle PDF editing.
How to Underline a PDF Using Smallpdf
1. Visit the Smallpdf website in your browser.
2. Click “Edit PDF” and upload your document.
3. Select the Annotation Tool and choose the Underline option.
4. Drag your cursor over the text you want to underline.
5. Click “Apply Changes” and download your updated PDF.
✅ Pros:
✔ Fast and easy-to-use interface.
✔ Supports cloud storage integration (Google Drive, Dropbox).
✔ No need to install software.
❌ Cons:
✘ The free version has a limit on the number of edits per hour.
✘ Requires a paid subscription for advanced features.
3. Sejda PDF Editor – Edit Text and Annotations Online
Sejda PDF Editor is one of the few online tools that allows users to edit both text and annotations. This means you can not only underline existing text but also add new text if needed.
How to Underline a PDF Using Sejda
1. Open the Sejda PDF Editor website.
2. Click “Upload PDF” and select your document.
3. Choose the Underline Tool from the toolbar.
4. Select the text and apply the underline effect.
5. Click “Download” to save the updated document.
✅ Pros:
✔ Allows text editing in addition to annotations.
✔ Supports multiple PDF editing tools (merge, split, sign, etc.).
✔ No software installation needed.
❌ Cons:
✘ Free version limits file size and number of edits per day.
✘ Some features require a premium plan.
4. DocHub – Google Drive Integration for PDF Markups
If you frequently use Google Drive and need a PDF editor with seamless integration, DocHub is a great choice. It allows users to underline text, add comments, and sign documents directly within Google Drive.
How to Underline a PDF Using DocHub
1. Open Google Drive and find the PDF file you want to edit.
2. Right-click on the file and select “Open with” > DocHub.
3. Click on the Underline Tool from the toolbar.
4. Drag the cursor over the text to apply the underline.
5. Click “Save” to store the edited PDF in your Google Drive.
✅ Pros:
✔ Direct integration with Google Drive for easy access.
✔ Allows collaboration (multiple users can edit the same PDF).
✔ No software installation required.
❌ Cons:
✘ Requires a Google account to access features.
✘ Free version has limited daily usage.
If you just need basic underlining, PDF4Sure and Smallpdf are perfect free options. If you want more editing flexibility, Sejda PDF Editor lets you modify both text and annotations. For those who use Google Drive for document management, DocHub is the best choice.
With these free tools, you can underline PDFs online anytime, anywhere—without spending a dime!
Mobile Apps for Underlining PDFs
With the rise of mobile productivity, editing PDFs on the go has become more important than ever. Whether you’re a student, professional, or casual user, having a mobile app that lets you underline PDF text can save time and effort. Below are some of the best mobile apps for underlining PDFs, along with step-by-step instructions on how to use them.
1. Adobe Acrobat Mobile App (iOS & Android)
Adobe Acrobat is one of the most trusted and widely used PDF apps. The free version allows you to view, annotate, and underline text, while the premium version offers more advanced editing features.
How to Underline Text in a PDF Using Adobe Acrobat Mobile
1. Download and install the Adobe Acrobat Reader app from the App Store or Google Play.
2. Open the PDF file you want to edit.
3. Tap on the “Comment” tool (looks like a speech bubble).
4. Select the Underline tool (a straight line symbol).
5. Drag your finger over the text you want to underline.
6. Tap “Save” to keep your changes.
✅ Pros:
✔ Easy to use with a familiar interface.
✔ Works seamlessly with Adobe Cloud.
✔ Free version allows basic annotations.
❌ Cons:
✘ Requires an Adobe account to save and sync files.
✘ Some advanced features need a paid subscription.
2. Xodo PDF Reader & Editor
Xodo is a free and feature-packed PDF reader that allows you to underline, highlight, and annotate PDFs effortlessly. It also offers real-time collaboration, making it perfect for teams and students.
How to Underline Text in a PDF Using Xodo
1. Download and open the Xodo PDF Reader app.
2. Tap on “Open Document” and select your PDF.
3. Tap the pencil icon to access annotation tools.
4. Select “Underline” and choose your preferred color.
5. Drag your finger over the text you want to underline.
6. Tap “Save” to keep the changes.
✅ Pros:
✔ Completely free with no hidden costs.
✔ Supports Google Drive and Dropbox integration.
✔ Works offline without requiring an internet connection.
❌ Cons:
✘ Some features might feel overwhelming for new users.
✘ Doesn’t offer advanced text editing like premium apps.
3. Foxit PDF Editor (iOS & Android)
Foxit PDF Editor is a lightweight but powerful alternative to Adobe Acrobat. It provides an easy way to underline and annotate PDFs while offering additional features like text editing and signing documents.
How to Underline Text in a PDF Using Foxit PDF Editor
1. Download and install Foxit PDF Editor from the App Store or Google Play.
2. Open your PDF file.
3. Tap the annotation tools (usually in the top menu).
4. Select “Underline” and choose a color.
5. Drag your finger over the text you want to underline.
6. Tap “Save” to apply your changes.
✅ Pros:
✔ Supports text editing in addition to annotations.
✔ Works with cloud storage services.
✔ Lightweight app that runs smoothly on most devices.
❌ Cons:
✘ Some advanced features require a paid version.
✘ Interface isn’t as user-friendly as Adobe Acrobat.
If you need basic underlining and annotation, Xodo PDF Reader is a completely free and easy-to-use option. For more professional editing, Adobe Acrobat and Foxit PDF Editor provide additional tools like text editing and document signing. No matter which app you choose, these mobile solutions ensure that you can underline PDFs anytime, anywhere—right from your smartphone!
Advanced Editing: Directly Underlining PDF Text
While most PDF editors allow you to annotate PDFs by adding an underline, advanced PDF editors go a step further—they let you edit the actual text within the PDF and apply underlining just like you would in a Word document. This method is useful when you want to make permanent formatting changes rather than just annotations.
How Advanced PDF Editors Allow Direct Text Underlining
Unlike annotation tools that overlay an underline on the document, advanced PDF editors modify the text itself, allowing you to:
✅ Underline text directly within the content.
✅ Change font styles, colors, and sizes in a PDF.
✅ Make permanent changes rather than temporary annotations.
✅ Edit other text elements (bold, italics, strikethrough).
These features are available in premium PDF editors like Adobe Acrobat Pro, PDF-XChange Editor, and Nitro PDF.
When to use direct text underlining?
- When you need permanent text formatting changes.
- When the document is professionally formatted (e.g., legal contracts).
- When working on PDFs that will be printed with proper text styling.
When to use annotation-based underlining?
- When you want a temporary or removable underline.
- When reviewing or collaborating on documents.
- When the PDF does not allow text editing (e.g., scanned PDFs).
Recommended Tools for Direct Text Underlining
1. Adobe Acrobat Pro
- Open the PDF in Adobe Acrobat Pro.
- Click “Edit PDF” from the tools menu.
- Select the text you want to underline.
- Click the Underline button in the formatting options.
- Save your file with the updated underlined text.
✅ Best for professional PDF editing.
❌ Requires a paid subscription.
2. PDF-XChange Editor
- Open your PDF in PDF-XChange Editor.
- Click on the Edit Tool and select the text.
- Choose Underline from the font styling options.
- Save the changes.
✅ Lightweight and fast.
❌ Some features require a Pro version.
3. Nitro PDF
- Open the PDF in Nitro PDF.
- Click on Edit > Format and choose Underline.
- Apply the change and save the document.
✅ Great alternative to Adobe Acrobat.
❌ Not available for Mac users.
If you need permanent underlining within the actual text of a PDF, advanced PDF editors like Adobe Acrobat Pro, PDF-XChange Editor, and Nitro PDF are the best options. However, for quick markups, using annotations may be a more flexible and reversible solution. Choose the method that best suits your workflow!
Conclusion: Master PDF Underlining
Underlining text in a PDF might seem tricky at first, but with the right tools and techniques, it becomes an easy and effective way to highlight important information.
Quick Recap:
✅ Basic underlining: Use annotation tools in Adobe Acrobat Reader, Xodo, or Foxit PDF.
✅ Direct text underlining: Requires advanced PDF editors like Adobe Acrobat Pro or Nitro PDF.
✅ Scanned PDFs: Need OCR conversion before you can underline actual text.
Whether you’re a student taking notes, a professional reviewing documents, or just someone who likes organizing information, knowing how to underline text in a PDF can improve your workflow. Choose the right tool for your needs and underline PDFs like a pro!
FAQs: Common Issues & Fixes
When working with PDFs, underlining text might not always be as straightforward as expected. Below are answers to some frequently asked questions about underlining PDFs, along with solutions to common issues.
1. Why Can’t I Underline Text in My PDF?
There are a few reasons why you might not be able to underline text in a PDF:
- The PDF is scanned or image-based, meaning there’s no selectable text.
- The file has editing restrictions preventing modifications.
- You’re using a basic PDF viewer that lacks annotation or editing tools.
Fix:
- Use an OCR (Optical Character Recognition) tool like Adobe Acrobat or PDF4Sure to convert scanned PDFs into editable text.
- Try a different PDF editor that supports underlining, like Xodo or Foxit.
- Check if the PDF has security settings restricting editing and adjust them if possible.
2. How Do I Remove Underlining from a PDF?
If the underline was added as an annotation:
- Open the PDF in your PDF editor.
- Select the annotation tool (comment or markup section).
- Click on the underlined text and delete the annotation.
If the underline is part of the actual text formatting:
- Open the PDF in Adobe Acrobat Pro or Nitro PDF.
- Use the Edit PDF tool, select the text, and remove the underline.
3. Can I Change the Underline Color?
Yes! Most PDF annotation tools allow you to change underline colors. Here’s how:
- Select the underline annotation.
- Look for color settings (usually in the toolbar).
- Choose your preferred color and save the changes.
4. What’s the Best Free Tool for Underlining PDFs?
If you need a free option, Xodo, PDF-XChange Editor, and Smallpdf are great choices.
- Xodo: Free and works on both desktop and mobile.
- PDF-XChange Editor: Offers advanced free annotation features.
- Smallpdf: Simple web-based tool for quick markups.
5. Can I Underline in a Scanned PDF?
Since scanned PDFs are essentially images, you can’t directly underline text. However, you have two options:
1. Use OCR software (like Adobe Acrobat Pro or PDF4Sure) to convert it into searchable text.
2. Use an annotation tool to draw an underline manually.