How to highlight text in a PDF in seconds: Complete guide for desktop & mobile

Highlighting PDFs requires selecting text and applying a color overlay using annotation tools. The three primary methods are: (1) Online editors like pdfFiller (no installation, works on any device), (2) Desktop software (offline access, advanced features), and (3) Built-in apps like Mac Preview (free, basic features). Common highlighting issues include scanned or image-based PDFs (which require OCR), security restrictions, file corruption, and using basic PDF readers without annotation tools. For complex documents, use a color-coding system to stay organized (e.g., yellow for key points, red for errors, green for approvals).

• Highlighting text in a PDF helps you emphasize key information, reducing document review time by up to 40%.
• You can highlight PDFs using online editors like pdfFiller, desktop software, or built-in apps like Mac Preview. Online tools offer the most flexibility, with no installation needed.
• Combine highlights with underlining, strikethrough, and comments to make your feedback clear and actionable.
• If you can’t highlight a PDF, it might be a scanned image or have security restrictions. Use an online tool with OCR technology to make the text selectable.
• Use a color-coding system (e.g., yellow for key points, red for action items) to keep your documents organized and easy to navigate.

Highlighting text in a PDF is a common need for students, professionals, and anyone working with digital documents. Whether you’re studying for an exam, reviewing a contract, or collaborating on a report, emphasizing key information is crucial. Digital document annotation, including highlighting, underlining, and commenting, streamlines collaboration and review processes.

So, how can you efficiently mark text in PDF documents? Check out our guide, which provides you with simple, step-by-step instructions and tips on how to highlight text in a PDF document using pdfFiller, a professional online tool for any document management need.

What is highlighting in a PDF?

Highlighting in a PDF is a digital annotation feature that allows you to apply a transparent color overlay to text, much like using a physical highlighter marker on a printed page. Portable document format highlighting allows users to emphasize text without altering the original content. It is a fundamental PDF markup tool used for studying, reviewing, and collaborating on documents.

This function is critical for:

• Efficient PDF highlighting and review
• Identifying key clauses in a legal document
• Marking essential data points in a business report
• Adding notes or comments related to the highlighted area.

Unlike simply changing the text color, highlighting keeps the original text visible and adds a layer of color over it. This makes it an excellent, non-destructive way to draw attention to specific content without altering the document’s original state. Using a PDF text highlighting tool makes it easy to add or remove these marks as needed.

What are the different methods for highlighting a PDF?

There are several ways to highlight text, each with its own advantages for convenience, features, and security. Let’s review the most common methods to help you find the best PDF editor with highlighting for your needs.

For most users, an online PDF highlighter tool like pdfFiller offers the perfect balance of robust functionality and ease of use. It provides a simple way to properly annotate PDFs without Adobe on any device, without installing or managing software.

Can I highlight PDFs on mobile?

Yes, you can highlight PDFs on your mobile device with pdfFiller. Access and edit your documents directly from any mobile browser, or install the pdfFiller app for iOS and Android to highlight, annotate, and manage your PDFs on the go. Both options let you work on your documents from any device or location.

Before you start

To highlight your PDF smoothly, quickly check these requirements before you start:

• Supported file formats: pdfFiller works with PDFs, Word documents (.doc, .docx), PowerPoint files (.ppt, .pptx), Excel spreadsheets (.xls, .xlsx), and image formats (JPG/JPEG and PNG). If you try to upload unsupported formats, they won’t load, but you’ll get a clear message.
• Allowed file size: You can upload PDFs up to 100 MB and other file types up to 25 MB. If your file is too large, you’ll need to split or compress it before uploading.
• Browser compatibility: pdfFiller runs smoothly in any browser, like Chrome, Firefox, Edge, and Safari. Make sure your web browser is up to date for the best editing experience.
• Valid subscription: To edit and manage documents in pdfFiller, you need an account and a subscription plan. If you are a new user, sign up for a 30-day free trial to test our platform’s functionality.
• Internet connection: pdfFiller works online through a web browser, so ensure that your device has a stable internet connection before uploading or editing any documents.

What other PDF annotation tools can I use besides highlighting?

Highlighting is just one of several PDF annotation tools available to help you mark up and edit PDF files. Effective document review often involves a combination of different PDF markup tools to convey clear and specific feedback. Combining these tools can make your edits much more effective.

Here are some other ways to create secure PDF text marks in pdfFiller:

• Underline: Use this to draw attention to text without obscuring it with color. It’s a more subtle way to emphasize a point.
• Strikethrough: This tool draws a line through text, which is the standard way to indicate that particular content should be deleted or is no longer relevant. It’s especially useful for collaborative editing.
• Comments and sticky notes: These tools allow you to add comments or questions to a specific part of the document without cluttering the page itself.
• Draw freehand: Drawing tools let you circle content, draw arrows to connect ideas, or make freeform marks directly on the PDF page.

As you can see, pdfFiller provides a full suite of these tools, enhancing your ability to communicate clearly when working on a PDF document.

How do I highlight text in a PDF document using pdfFiller?

pdfFiller makes it simple and easy to mark text in PDF documents from any device. It provides a straightforward online PDF highlighter that works across all operating systems without requiring a software download. In addition to being a powerful PDF editor with highlighting capabilities, pdfFiller offers a full suite of editing, annotation, and collaboration tools in a secure environment.

Simple steps to highlight PDF content easily and quickly using pdfFiller

1. Open your PDF file in the editor

• Once logged in, click Add new to upload a file from your device, cloud storage, email, or a secure document URL.
• Once uploaded, the file will automatically open in our editor, ready for adjustments.

A screenshot of pdfFiller’s Dashboard displays how clicking the “Add new” button and selecting “Upload document” reveals a dropdown menu with file upload options from a device, cloud, URL, or email.

2. Activate the Highlight tool

• Click Highlight on the editing toolbar at the top of the page.
• Choose a simple or rectangular highlight tool and click the color swatch.
• Select the color, line thickness, and density for efficient PDF highlighting.

A screenshot of pdfFiller’s Highlight tool that allows you to customize your document with adjustable color, line thickness, and density settings for precise and clear markups.

3. Select and emphasize text in PDF

• Move your cursor over the text in a PDF you want to mark.
• Drag the cursor across the text and move the highlighter to cover the entire section you want to mark.
• Click OK to apply text emphasizing or use the Trash icon to cancel the marker.

4. Use other tools for highlighting

• Use the Line option to underline particular words or phrases with the desired color.
• Click Draw to circle content or create other freehand marks.
• Click the Arrow tool to point to the specific place in the document where you need further corrections. 

5. Save the updates

• Click the Done button at the top right corner of the screen once you finish editing.
• Download the edited file, export it to a cloud storage, print it, or share it securely with others via email or fax.

pdfFiller is the best PDF highlighter for students, business professionals, and legal teams, offering tailored features for every need at a reasonable price.

Why can’t I highlight text in my PDF?

Can’t select text in your PDF? It’s a common issue, especially when you need to quickly mark up a document for a project or course. Understanding why you can’t select or highlight text is the first step to fixing it.

Let’s review the most common reasons you can’t highlight a PDF and how to fix them.

Scanned documents (PDF as an image)

The most frequent reason is that the PDF is “scanned” or “image-based.” This means the document is essentially a collection of images of pages, not actual text. Because the software sees pixels instead of characters, you can’t select the text to highlight it.

Solution: You need a tool with optical character recognition (OCR) functionality. OCR scans the image of the text and converts it into selectable, editable text.

Security restrictions

Sometimes, the creator of the PDF file may apply security settings that restrict editing and commenting. As a result, these permissions prevent you from making any changes, including adding annotations like highlights or notes.

Solution: Contact the document owner, asking to share an unlocked PDF version or grant you permission to make changes. Alternatively, you can use specialized tools that can remove certain restrictions legally.

Read our guide to learn how to unlock a PDF and take full control of your documents.

Corrupted file structure

Damaged PDF files may display content but fail to recognize text properly, making selection and highlighting impossible. File corruption can occur during creation, transfer, or conversion between formats.

Solution: If a file’s structure is corrupted, consider converting the PDF to another format (for example, convert PDF to Word). This approach can help address underlying issues and enable accurate text recognition.

Using a simple PDF reader

Some basic PDF readers lack annotation functionality altogether. Free viewers may only support reading without offering tools for creating highlights, comments, or other markup elements.

Solution: Choose a professional PDF editor like pdfFiller, offering a comprehensive suite of tools for document editing, electronic signatures, sharing, and collaborative workflows.

Tips on creating a color-coded highlighting system

Now you know how to use an online PDF highlighter. But what if your paperwork is lengthy and requires multiple annotations and highlights? Using a particular color system will help better organize the document and improve consistency and communication across your team. Here are some expert tips on efficient PDF highlighting:

• Define color meanings upfront: Establish what each highlight color represents. Document these conventions and share them with all reviewers. For example, yellow usually stands for general importance or key points, green represents approved content or completed items, blue means that the content requires verification or fact-checking, and red indicates errors or mistakes that need corrections.
• Adapt colors to your industry: Different fields benefit from specialized color systems. Legal teams might use colors to distinguish different contractual terms—indemnification clauses, payment terms, termination conditions. Academic researchers might use color codes by theme—methodology, results, discussion, or limitations.
• Maintain consistency: Once you establish a color system that works, apply it consistently across all documents and projects, and communicate it with your team. This consistency makes document review faster and more intuitive over time.
• Combine highlighting with comments: A clear color system is helpful, but adding brief comments to highlighted sections enhances context and clarity. This approach fosters a deeper and more comprehensive understanding of the information being conveyed.

Final thoughts

Learning how to highlight text in a PDF is a simple skill that can greatly improve your productivity. Whether for personal study or professional collaboration, using an online PDF editing tool like pdfFiller provides a fast, secure, and versatile solution. You can not only highlight but also underline, strikethrough, and add comments to any PDF document from any device.

By choosing a tool that handles everything from basic highlighting to advanced features, you streamline your entire document workflow. pdfFiller is designed to ensure secure PDF text marks and is compliant with leading industry standards, making it ideal for managing sensitive files.

Ready to experience efficient PDF highlighting and editing?

Start your free trial with pdfFiller today and gain access to a full suite of powerful document management tools.

Glossary

• Annotation: A note, comment, or mark (such as a highlight) added to a document to provide feedback or emphasize information. Annotating is the act of adding these marks.
• Markup: The process of adding annotations to a document. Markup tools include highlighters, pens, and comment boxes.
• Strikethrough: A PDF annotation tool that places a line through the center of select text in a PDF document to indicate it should be deleted or is no longer relevant.
• OCR (Optical Character Recognition): A technology that converts images of typed, handwritten, or printed text into machine-encoded, searchable text. This is essential for highlighting scanned PDFs.
• PDF reader: A software application used primarily for opening and viewing PDF files. Many free readers have very limited or no editing or annotation functionality.
• Toolbar: A row of buttons or icons in a software application that provides quick access to commonly used functions or tools, such as the highlight button or text tools.