PAPER by FiftyThree: SKETCH, DIAGRAM, TAKE NOTES (mobile)
When inspiration happens, put it on Paper. Paper is the best way to capture and connect your notes, photos, and sketches. Create checklists, spotlight details in photos, and sketch diagrams with unbeatable speed and ease — Paper is like a wall of sticky notes for everything that inspires you.
Folia is the professional way to share documents for feedback and discussion. Stop printing, avoid lengthy email threads, modernize meetings, and more. Our state of the art annotation and commenting tools enable deep conversations, so you can be more effective with your content.
XODO DOCS (mobile/web)
Even if you use a PDF management system like Sente or Papers, it is a good idea to have a standard PDF reader on your iPad to process files that should not clutter your research database: Committee work, conference programs, call for papers, syllabi and so on. Xodo is my weapon of choice for this, mainly because it was the first one that supported annotations. If you want more options, check out the guide to annotating PDFs for more iPad apps that do essentially the same thing.