PDF files are everywhere on the web, and remain an excellent format for documentation that needs to retain its fonts and formats. Chrome OS does a great job of viewing PDFs, but you’ll need to dig a little further if you want to add notes or edit files.
Built into Chrome
Chrome has a built-in PDF viewer that’s fast and very easy to use – it simply treats PDFs on the web like a regular web page. You can go fullscreen for distraction-free reading.
Preview from Google Drive
There’s also a previewer in Google Drive – use it by clicking on any of your PDFs from Drive’s web interface. It’s slightly faster than the built-in Chrome viewer, because it doesn’t download the the full file, but dithers graphics and shows a lightly rendered version, which is great for huge PDFs and less stable internet connections.
PDFZen is a fully online PDF editor, which will let you do notes, comments, highlights and drawing on a PDF, which you can then download or share with anyone, and you don’t even have to log in. The only thing you can’t do is actually edit the text of a PDF file, so this is more for annotating an existing document (e.g. class notes) than re-editing.
PDFescape is very similar to PDFZen, with similar capabilities and similar tools, but a slightly different interface.