20 Free Tools to Annotate PDF Documents

Do you use PDF files or read documents in PDF format? Even if you don’t use them regularly, I’m sure that you’ve come across a PDF file or two in your lifetime. They’ve been around for over 20 years and can contain links, buttons, form fields, videos, audio and more.

Reading PDF files can be done in many applications, but a lot of those apps don’t include annotation tools. In this post we’re going to focus on apps that do allow you to annotate PDF files. Whether you want to add text notes, bookmark a section, highlight or underline text, these free tools will allow you to do just that.

Shortcut to PDF annotation tools for:

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iPhone/iPad

Adobe Reader

This is the official Adobe Reader mobile application which works for the iPhone and iPad. It can also be used to fill out forms and electronically sign documents. With it, you can: highlight, strikethrough, underline, draw (freehand), comment (sticky notes) and add text using the typewriter tool.

Adobe Reader for iPhone and iPad
PDF-Notes free for iPad

This is the free version of the premium app pdf-notes; it’s available for the iPad only. Along with support for AirPrint, you can annotate your PDF files using a variety of pens, highlighters and text notes. It includes smooth finger writing and a palm rest so that there are no accidental marks on your documents.

pdf-notes free for iPad
UPAD Lite

UPAD Lite is an advanced note-taking application with annotation features. You can handwrite notes, highlight text, add sticky notes and reference images. UPAD uses smooth retina ink, which results in beautiful, detailed handwriting. You can export any type of document as a PDF or PNG file by email or to cloud services like Dropbox, Evernote and Google Drive.

UPAD Lite for iPad
Mendeley

Mendeley is a companion app to the desktop tool for Windows. You’ll get your own digital library so that you can read, annotate and organize all types of files including PDF. Mendeley includes many features such as citation and bibliography generation, sticky notes and highlighting, importing and organizing PDF files, collaboration with a team, and much more.

Mendeley for iPhone and iPad
PDF Max

The free version of PDF Max is great for annotating, filling in forms and taking notes. At this time, it’s the only iOS PDF application that supports Adobe’s Rich Text Format Typewriters (aka FreeText). You can annotate by highlighting, underlining, crossing out and using "squiggly tools." It also supports addition of comments and threaded conversations, great for collaboration.

PDF Max for iPhone and iPad
DocAS Lite

The free version of DocAS lets you annotate PDF files, sketch ideas, create presentations, record audio clips and share notes. You can also access documents anywhere: PC/Mac desktop (via wifi), Dropbox, Box, Google Drive, FTP, WebDAV, other iOS apps and more. As well as PDF files, DocAS supports Microsoft Office and Apple iWork files, RTF, text and photos.

DocAS Lite for iPad

Android

Adobe Reader

Just like Adobe Reader for iOS, the Android version lets you view, annotate, comment, fill out, electronically sign and share documents. It has all of the same features as the iOS app like freehand drawing, highlighting, underlining, etc.

Adobe Reader for Android
qPDF Notes Demo

Although this is only a demo of qPDF Notes, it includes all features available in the full version; however, a watermark will be added to your PDF files if exported – which is fine for personal use or trying before you buy. With qPDF Notes you can add text, sticky notes and shapes to your PDF files. You can also highlight, cross out, underline, and sign documents.

qPDF Notes for Android

Web/Browser

Need annotation tools that work on the Web? Try these on for size.

A.nnotate

A.nnotate is great for those wanting to annotate images, PDF files and Microsoft Office documents online. With it, you can add text notes, highlights and strikethrough. The collaboration feature with threaded comments and the ability to add tags to notes, makes A.nnotate great for freelancers, small teams and even businesses.

Annotate for Web
PDFescape

PDFescape is not only great for editing and annotating PDF documents, but you can also create new PDF forms, fill out PDF forms, password protect your files and share documents. With PDFescape, you can add text comments, shapes, images, sticky notes, and highlights to documents. Check out many other advanced features PDFescape has.

PDFescape for Web
GroupDocs

GroupDocs is an advanced document collaboration tool that includes annotation features for PDF and Microsoft Office documents. You can add comments and mark up your text in real-time, much like documents in Google Drive. GroupDocs has 3 paid plans, and a free 14-day trial plan that lets you try before you buy.

GroupDocs for Web
PDFOnlineReader

PDFOnlineReader is not just for reading PDF files online. You can also add annotations, add hyperlinks and bookmarks, and highlight text. It’s a lot simpler to use and it’s great for those who want to annotate quickly, save and download their files. It also offers PDF desktop products for batch PDF creation and converting PDF files to other formats (and vice versa).

PDFOnlineReader for Web

What do you use?

Now that we have shared 20 free PDF annotation tools for iOS, Android and the Web, it’s your turn. Do you use a free or paid PDF annotation tool? Which tool do you use and for which platform?

Want to learn more about PDFs? Read our Mastering PDF: 80 Free Tools, Tips and Resources.

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