In history classes I have often had students read primary source documents or copies of them in PDF format. For many students the challenge of reading primary source documents is understanding the vocabulary and or the context of those documents. If you have students use PDF annotation tools they can add questions and notes to documents as they read. When they share those annotated PDFs with you, you have a ready source of discussion questions. Here are three services that your students can use to comment on PDFs.

Marqueed is a service that allows users to create and discuss collections of images and PDFs. Using Marqueed you can highlight and draw on images as well as PDFs. You can share MarQueed files or keep your files private. Likewise you can create private and public collections of files.

If you upload a PDF to Google Drive, you can add comments to it. That comments won’t be attached to specific parts of the PDF. The comments will appear in right-hand margin under the comments button.

Crocodoc is a simple service that allows users to quickly share and edit PDFs, Word documents, and PowerPoint files.To use Crocodoc just upload your file, select your marking tool, and get to work. Crocodoc provides a unique url for every file you upload. Share that url with the people you want to have comment on your PDF, Word file, or PowerPoint slides. You can also embed your file into a blog post or webpage and allow people to comment on it there.