Adobe Acrobat Reader (free and paid accounts)
Adobe Acrobat allows users to highlight, add comment boxes, make freehand drawings or annotations, and add their signature to PDF documents.
- Documents can be saved to the Adobe Document Cloud for access across multiple devices. Accounts are free and include 2 GB storage space. Paid accounts with more features are available.
- Comments are stored with user's name for easy collaboration - can easily tell who said what.
- When sharing via email, documents can be flattened so that annotations can be seen when the PDF is opened in other programs.
The Reader/Acrobat DC Forum for Mobile Devices provides answers to some of the most commonly asked questions about this program.
Evernote and Skitch (free and paid accounts)
Evernote is a robust note taking program that comes in both free and premium versions. It's compatibility with a wide variety of platforms makes it a popular program. Skitch is a companion to Evernote, and must be used in order to annotate PDFs.
- Free Evernote accounts limits users to 60 MB of data per month and syncing of only 2 devices. This could limit Evernote's functionality if you are annotating many documents or ones that are very large.
- Premium Evernote accounts are available for $34.99/year and $69.99/year. Users are allowed up to 1 GB or 10 GB of data each month (respectively), have access to addition features such as offline notebooks, and almost any file type is supported.
- Direct PDF annotation is only supported with the $69.99/year premium account.
- To annotate PDFs using Skitch the files must first be uploaded into an Evernote account, then opened in Skitch.
For more information on how to use Evernote, check out The Beginner's Guide to Evernote and How to Use Evernote: The Unofficial Manual, as well as the Getting Started with Evernote page.
Folia (free and paid accounts)
Designed with collaboration in mind, Folia supports a large number of file formats and supports real-time editing. Allows syncing across multiple devices and now offers features for annotating within a web browser.
- Integrates with Box, Dropbox, Google Drive, and OneDrive.
- The free version allows up to 25 documents and sharing with up to 25 people. Paid plans with advanced features are also available.
Folia has a helpful Support Forum available online.
GoodNotes lets you take handwritten notes and annotate PDF documents. Notes can be synced across devices using iCloud.
- Handwritten notes can be turned into searchable text.
- Notes can be backed up to other cloud storage programs.
- GoodNotes can be used as a digital whiteboard for teaching or presentations.
Follow the GoodNotes Blog to stay updated on the newest features. There is also a helpful online Support Forum available.
iAnnotate PDF ($9.99)
Despite the name, iAnnotate PDF allows for annotation of multiple document types, such as Word, PowerPoint, and images.
- Attach multimedia files, such as images, to documents.
- Record short audio clips of up to one minute.
- Annotations can be reviewed in a searchable list.
The iAnnotate PDF Support Page has lots of information and answers to commonly asked questions about the app.
Microsoft OneNote (free)
OneNote is available on a variety of platforms and can be used to take notes and annotate many different file types.
- Features and controls are similar to those in other Office products, such as Word, so familiar working environment for many users.
- Collaboration tools allow easy sharing and editing of documents with others.
- Requires a free Microsoft account to use. Notes will be stored in the cloud in this account and can be synced across multiple devices.
- To annotate files on mobile devices, they must first be inserted into a note on a laptop or desktop. Documents can be inserted into OneNote one of two ways: 1) Open the Print menu in the document and select 'Send to OneNote' as the printer, or 2) Open a note in OneNote to add the document to and choose 'File Printout' in the Insert menu. These notes can then be synced to the mobile device through a Microsoft account and opened in the app.
The OneNote FAQs have answers to common questions about using the apps and Office News has details on updates to the desktop and mobile apps.
Notability combines easy-to-use note taking features with powerful organization. The app is available on all iOS devices and notes are synced through iCloud.
- Annotate multiple file formats. Organize notes and group by subject.
- Record audio and link to contents in a note.
- Search both note titles and content to find information.
- Purchase once and download to all iOS devices at no extra cost.
The Notability Support Portal provides answers to commonly asked questions about the app.
Whink has 3 distinct note taking modes to choose from: Write, Type, and Read.
- Write mode provides a natural handwriting experience with your finger or a stylus.
- In Type mode select from tasteful fonts and colors to type notes anywhere on the page.
- The Read mode removes writing tools from view and provides you with just a simple highlighter to mark text.
Whink has a helpful Online Support Forum.
Xodo is a free, cross-platform PDF viewer and annotator that is optimized for all phones and tablets. Allows for accessing, marking up, sorting, sharing, syncing, and managing PDF documents.
- Annotate PDFs with highlighting, underlining, striking out passages, adding sticky notes, inserting shapes, and drawing freehand. You can also fill forms and add your signature to documents.
- Collaborate in real time with others.
- Directly access PDFs in Dropbox and Google Drive and sync across devices.
Follow the Xodo Blog to stay up-to-date on new features. Help is available in the online Support Forum.