Adobe Acrobat Reader (free and paid accounts)
Adobe Reader for laptops and desktops is more limited in annotation functionality than its mobile versions. Users are limited to highlighting text and adding comment boxes to a document.
- Freehand drawings and annotations are not supported.
- 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 Adobe Reader Forums provide answers to some of the most commonly asked questions about this program.
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. PDF annotation is only supported with the $69.99/year premium account.
- 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.
Microsoft OneNote (free with Microsoft Office Suite)
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.
- Offers Optical Character Recognition (OCR) to extract text from pictures
- Requires a free Microsoft account to use. Notes will be stored in the cloud in this account and can be synced across multiple devices.
- Documents can be inserted into OneNote for annotating 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.
The OneNote Quick Start Guide (PDF) highlights features of the current version of OneNote. The Beginner Geek: Getting Started with OneNote 2010 article is about the previous version but has many tips that are useful for the current one.
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. In addition to the web app a Chrome Extension is also available.
- 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.