How to Underline in PDF for Free

Summary :

Underlining is crucial for highlighting important information. In this guide, we will explore how to underline in PDF using free and easy methods.

Table of Contents

How to Underline in PDF

How to Underline in PDF

Usually during reading, underlining plays a crucial role in emphasizing relevant content and promoting understanding. Whether you want to emphasize a point, highlight important information, or improve the clarity of your PDF, adding underlining to your PDF is the best option.

In this article, we will explore effective ways to add underlines to help you achieve your goal easily, and a free option is provided.

👉 To get started, get PDFgear, the best free PDF underline software.

How To Underline PDF With PDFgear

PDFgear is the best free alternative to Adobe Acrobat Pro that allows you to underline and edit PDFs for totally free.

FREE PDF Underline Software

Free to underline, strikethrough, and highlight text in PDF documents for free on computer and mobile.

Support is available across a variety of platforms, including Windows, macOS, and iOS. PDF editing, creation, and conversion can be easily achieved. It can maximize the efficiency and convenience of using PDF.

Step 1. Open PDF

Download PDFgear and install it on your device, then click “Open File” and select the PDF you need to edit.

Open PDF in PDFgear

Open PDF in PDFgear

Step 2. Enter Comment Mode

Click “Annotate” > “Underline” in the upper toolbar and select the color of the underline.

Check Underline Banner

Check Underline Banner

Step 3. Select Text that Needs to Be Underlined

Move the cursor to select the text that needs to be underlined to add underline to the PDF.

Select Text

Select Text

Step 4. Save Edits

Click the “Save” icon in the upper left > Hit “Exit Editing”.

Save Changes

Save Changes

PDFgear also provides very comprehensive PDF editing functions. Just click “Edit” on the upper toolbar to make the PDF editable, and easily add text, edit text, and add signatures in the PDF.

How To Underline in Adobe

Adobe Acrobat is one of the leading tools for working with PDFs, supporting reading, creating, and editing PDFs. Its versatility and advanced features make it a popular choice among professionals and students. Its comprehensive editing features allow you to underline in PDF very easily.

In addition to this, the program also allows you to edit text, add images, and more.

Step 1. Open your PDF file in Adobe Acrobat.

Step 2. Click “Tool”> In the toolbar in the upper left corner and select “Edit PDF”.

Enter Edit Mode

Enter Edit Mode

Step 3. Place the cursor in front of the text you want to underline, and drag the cursor to select the text you want to underline. Click the “underline” icon on the right toolbar.

Underline in PDF

Underline in PDF

This is the easiest way to add underlining in PDF, but this way is not suitable for all types of PDF files.

How To Underline PDF Online

We’ve explored desktop options, let’s move on to online solutions. PDFgear Online Editor is a practical and free tool that requires no download. Just open the PDFgear online editor in your browser to add text to PDF, edit text, etc.

This option is ideal for those who want to add underlines to PDF quickly and easily.

Step 1. Upload the Target PDF

Visit PDFgera Online Editor and click “Select File” to upload the PDF that needs to be edited.

Open PDF in PDFgear Online Editor

Open PDF in PDFgear Online Editor

Step 2. Enter Comment Mode

Click “Add or edit annotation” in the upper right toolbar > Tap on the “underline” icon.

Select Underline Icon

Select Underline Icon

Step 3. Select the Text that Needs to Be Underlined

Move the cursor to select the text to successfully add underlines to the PDF. If you want to change the underlined color, just click “Change Color” in the toolbar. This method also works for changing highlighted colors.

Select Text

Select Text

This method is convenient for users, but please note that it has a file size limit and only supports files under 20MB. For users who need to process large files, we recommend downloading PDFgear to enjoy processing PDFs without size and quantity limits.


Why Can’t I Underline in PDF?

There may be several reasons for not being able to add underlines in a PDF:

1. Make sure you are using the appropriate editing tool, such as Adobe Acrobat or PDFgear.

2. PDF documents may be password protected and restrict editing.

3. PDF documents may be scanned documents or image-based documents

How Do You Underline a PDF for Free?

Underlining in PDFs with PDFgear is completely free. Just download PDFgear > Open the PDF > Click “Annotate” > “Underline” icon > Select the target text to successfully add underlines and highlight important information.

How To Underline in PDF Online?

The best option for underlining PDF online is PDFgear Online Editor. Simply upload your PDF file and select the underline tool to add underlines to your PDF. You can do it directly in your browser, no need to install additional software.

Is It Possible To Change the Underlined Color in the PDF?

Yes, most PDF editing tools such as Adobe Acrobat and PDFgear allow you to customize underline color. Typically, you can choose from a variety of colors to highlight text based on your preference.


Underlining in PDF is an essential skill for improving understanding and highlighting key information in a document. With tools like Adobe Acrobat and PDFgear, you can quickly edit PDFs. Choose the tool that best suits your workflow and start underlining PDFs efficiently today.

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