How to easily underline text in PDFs with the PDF Reader app and alternatives

Android Guides » Android Apps » How to easily highlight text in PDFs with the PDF Reader app and alternatives

Reading and managing PDF files is a daily task in academic and professional life , and the ability to underline, highlight, and add annotations to these documents is essential for learning, organization, collaborative work, and personal productivity. While the experience of reading a PDF may not be the same as reading a physical book, current technology has incorporated advanced tools that allow you to easily underline, mark up, edit, and organize text in PDF files from any Android device.

Among the various options on the market, PDF Reader for Android stands out , an application that has surpassed ten million downloads thanks to its excellent combination of functionality, ease of use, lightweight design, and free access . In this article, you'll discover how to get the most out of PDF Reader for highlighting and annotating files , along with a comprehensive analysis of the most popular tools and alternative methods for highlighting, editing, and organizing your PDFs from your mobile device, computer, or even online.

Why choose PDF Reader to highlight and annotate PDFs?

The PDF format has become the universal standard for sharing, reading, and archiving digital documents . Unlike other file types, PDFs faithfully preserve the original design, fonts, and structure regardless of the device or operating system used to open them. However, editing or highlighting text in a PDF requires specialized tools that offer simplicity and efficiency.

PDF Reader for Android is positioned as one of the most complete and highly rated apps for those seeking a smooth experience that allows:

• underline texts in academic notes, manuals, articles, and ebooks to highlight key concepts and facilitate review.
• Annotate and highlight sentences or paragraphs important information with a single touch, ideal for study sessions, exam preparation or reviewing work documents.
• Add sticky notes, watermarks, text boxes, or comments anywhere in the document, promoting active learning and collaborative work.
• Organize your PDF library in folders, favorites and categories to find any file in seconds.

And the best part: all of this comes from a clean, intuitive interface, free of intrusive ads . This PDF reader is completely free and its use doesn't involve any annoying restrictions. Its lightweight design, compatibility, and speed make it an essential tool for both students and professionals.

Furthermore, its development focuses on ease of use for any user, regardless of their experience level. This means you can quickly access highlighting functions without wasting time in complicated menus or unnecessary settings.

How to underline text in a PDF with PDF Reader step by step

Highlighting text in a PDF file from your mobile device is easier than ever with PDF Reader . The process can be summarized in these steps, optimized to save you as little time as possible:

1. Open the PDF Reader application on your Android device and identify the PDF file you want to edit. You can find it from the recents list, the file explorer, or the favorites section.
2. Select the PDF document that you want to highlight and open it. Navigate to the specific page or section where the text of interest is located.
3. Tap and drag your finger over the part of the text you want to underlineThis can be done with individual words or entire paragraphs, adapting to the size of your screen.
4. Once the text is selected, the annotation tools pop-up menu will automatically appear. Tap the highlighter or highlight icon, depending on your goal.
5. The chosen text will be underlined or highlighted in the application's default color (usually green for underlining and yellow for highlighting). If you need to cross out or highlight in another way, select the corresponding icon.
6. Repeat this process on the different pages or sections where you want to make notes, with no limit on highlights or comments.
7. Once you finishSave your changes using the "Save" button in the app's top bar. This way, you'll be sure to retain all your notes and highlights for future reference.

The PDF file will be updated with the inserted marks and underlines, which you can view from any other compatible device. It's important to know that the default underline color in PDF Reader is usually green , and for now, color customization for this feature is limited. However, you can vary the type of annotation by switching between underlining, yellow highlighting, red strikethrough, and notes.

In addition, the tool allows you to add comments or sticky notes linked to each highlight , which is ideal for supplementing with explanations or clarifications that enrich the content.

If you overdo it with the underline or change your mind about a markup, you can delete any underline by selecting it and tapping the delete option in the context menu. This way, you'll always keep your PDF clean and tailored to your needs.

Additional features of PDF Reader for Android

Highlighting is just one of the many features that PDF Reader offers . To help you get the most out of this tool and make it your go-to PDF reader and editor, here's a list of its most useful advanced options:

• Advanced reading mode: Allows you to switch between vertical or horizontal scrolling, adjust the zoom to your preference, and activate night mode to reduce eye strain.
• Quick search for words or phrases within the PDF, making it easier to locate key concepts in long documents.
• File organizer: Ability to group, rename, move, or delete PDFs directly from the app, with viewing by folder, favorites, or recent history.
• Various notes: In addition to highlighting, you can add notes, insert custom text, include watermarks, perform strikethroughs, create bookmarks, or insert comments for group collaboration.
• Security features: PDF Reader allows you to password protect files to keep confidential documents private.
• Sharing and export options: Print, email, share on messaging apps, or even convert PDF to other supported formats.
• Multi-device synchronization, allowing your notes and highlights to stay up-to-date across multiple paired Android devices.
• Lightness and maximum compatibility: The app takes up less than 20 MB and consumes almost no resources, making it perfect even for entry-level phones or older tablets.
• Frequent updates which include bug fixes and new features, such as the addition of FAQs, the activation of interactive links, and improved user experience.

This combination of features covers virtually every need, from simple reading to advanced editing, making PDF Reader the best free option for editing and highlighting PDFs from Android.

Alternative methods to underline and highlight PDF on any device

While PDF Reader is the top choice for Android users , there are several alternatives for underlining, highlighting, and annotating PDFs on PCs, Macs, and through web browsers or online services . Below, we present a selection of the most recommended methods and tools based on your device and operating system:

1. From the computer: integrated tools and specialized editors

• Microsoft EdgeThe default browser in Windows allows you to open and highlight PDFs without installing anything. Simply open the PDF, select the text with the mouse, click the highlighter icon that appears, and choose the color. The context menu allows you to change the underline color or remove it, and you can save the changes to the original document or under a new name.
• Preview on MacmacOS users have access to the built-in Preview app to highlight and underline text in different colors, strikethrough, add notes, and customize markup in a very intuitive way, without relying on external software.
• Desktop applications such as Adobe Acrobat, Foxit Reader, PDFelement, PDF-XChange Editor or PDF CreatorAll of these applications offer advanced editing tools, highlighting, annotation, color changes, and much more. Some have free and paid versions, but they typically support signature insertion, commenting, document comparison, and form creation.

2. Online methods: web editors and browser extensions

• PDF2GO, SmallPDF, PDFfiller, PDF Buddy and FormatPDFThese are online platforms that allow you to upload PDF files, highlight, underline, add comments, and download the edited document without installing any software. Some include size or number of documents limitations in the free version, and offer additional features with a premium subscription.
• Chrome extensions like Highlighter or Kami: They install in your browser and allow you to highlight and annotate PDFs directly from the web. Kami even allows real-time collaboration, note-taking, and multi-color highlighting.

3. Convert to Word or Google Docs for advanced editing

• Convert PDF to Word or Google DocsSome online tools and office suites allow you to convert a PDF to a Word file or Google Doc. This allows you to freely underline, change colors, and format text, after which you can export the file back to PDF. This method is useful for text-heavy documents, but can cause formatting issues if there are complex graphics.

4. Alternative mobile apps to highlight PDF on Android and iOS

• Adobe Acrobat ReaderIn addition to reading files, it allows you to underline text, highlight, insert notes, add signatures, and collaborate. It's free, although advanced editing features require a subscription.
• Foxit PDF Reader & Editor: Powerful and multifunctional, it allows you to open, edit, underline, highlight and share PDF on both Android and iOS, being very popular especially in the Apple ecosystem.
• PDF element: One of the most comprehensive apps, it lets you underline, highlight, create and edit notes, add signatures, combine, crop, and rearrange pages, and password-protect files. It's available in both mobile and desktop versions.
• PDF reader and editor: Available on both systems, with a Word-like interface and features for highlighting, text editing, annotations, bookmarks, and signatures.
• Xodo PDF Reader & Editor: An optimal tool for group annotations, collaborative editing, and real-time highlighting, even integrated into some browsers.
• iLovePDF: It stands out for its simple interface, the ability to highlight in more than 20 languages, and other options such as conversion, editing, signatures, and annotations.
• PDF Reader - Annotate, scan and sign PDFs: Specialized in quick annotation and editing, with color and opacity adjustment for underlines.

Added benefits of highlighting PDF files on your device

• Facilitates learning: Highlighting key ideas or important data helps you retain knowledge better and review the most relevant information later.
• Improves productivity: The ability to mark tasks, comments, dates, or reminders directly on the document streamlines workflows and reduces errors.
• Allows for efficient organization: Annotating and highlighting content helps you structure presentations, write reports, or prepare for exams much more effectively.
• encourage collaborationSharing annotated PDFs allows multiple users to work on the same document, adding comments, questions, or contributions in real time or over time.
• Avoid printing and protect the environmentThe entire process is done digitally, eliminating the need for printing, which is more economical and environmentally friendly.

Common mistakes when highlighting PDFs and how to fix them

Occasionally, you may encounter PDFs that don't allow you to highlight or select text. Here we explain the most common causes and possible solutions:

• PDF based on scanned image (not selectable)If the PDF document was generated from a scanner or photo, the text is stored as an image and cannot be selected or underlined. The solution is to use an OCR (Optical Character Recognition) feature, available in apps like PDFelement or Adobe Acrobat, to convert the image into editable text.
• Security restrictions in PDFSome documents have permissions locked to prevent editing or annotation. You can unlock them with specialized tools, always respecting legal and privacy rights.
• Formatting issues when converting to Word or Google DocsIf you choose this method, the resulting file may contain layout or font errors. To minimize these issues, only use conversions on mostly text-based documents, and check the formatting before re-exporting to PDF.
• Apps that require a subscriptionAlthough many apps offer free highlighting features, some limit color customization or advanced editing to Premium users. Always check the terms and conditions before installing or subscribing.

Tips for highlighting and organizing your PDFs efficiently

• Use different colors for each type of information If your app allows it: For example, green for definitions, yellow for dates, red for warnings, etc.
• Do not underline excessivelyA document full of markup loses effectiveness. Limit yourself to key phrases or irreplaceable data.
• Complement underlining with notes: Adding a brief comment next to the underline can help you remember the main idea or its context when you review the document.
• Organize your PDFs into thematic folders and use the app's bookmarks and favorites to quickly categorize and access summaries, classes, papers, or digital books.
• Make regular backups to the cloud or sync between devices so you don't lose your notes.
• When working in a group, use share or export features so others can view and contribute to the same highlights.

These practices will optimize your digital study and work experience, allowing you to save time and be more efficient in your personal and collaborative organization.

There is no doubt that, although there are many ways and tools to highlight PDFs and each user can choose the one that best suits their needs, PDF Reader is positioned among the best free options on the market for Android due to the sum of all these advantages.

Using a PDF reader in your daily life will not only make studying and working easier, but will also allow you to have a more efficient, eco-friendly and versatile digital organization , adapted to any context, from your home, in the library, at work or during your travels.

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