If you're looking for a quick way to edit or sign a PDF document, there are free and easy-to-use tools for iOS, Windows, and Android devices.

Annotating a PDF can be compared to taking notes on a printout. You can underline things, add shapes, forms, and text, but you can't change the underlying PDF document itself.

Google may soon release a new PDF annotation feature for its Chrome OS PDF viewer. With the new feature, Chrome OS users can expect to draw and annotate their PDF documents using a mouse, touchpad ...

Thankfully, Chrome OS will soon have built-in annotation features, as a new flag for the functionality has appeared in the Dev and Canary branches.