Collaboratively Edit PDFs

Scribblar, a collaborative whiteboard platform that I've reviewed in the past, has recently announced support for PDFs. You can now upload PDFs to your Scribblar room. When you upload a PDF Scribblar will turn it into a editable image that you and your collaborators can alter. The free version of Scribblar will allow you to upload PDFs containing up to five pages.

Applications for Education
This announcement from Scribblar means that if you had older documents or drawings that you would like to have someone else alter you can do that. Scan a drawing, upload it Scribblar, and begin editing. This could be a fun way for art students to see how a change in color or a change of brush strokes alters a drawing or painting.