Over the last couple of days I tried Papers and PDF Expert on my iPad and iPad Pro, I have issues with both. With Papers, my main issues are: -- one can't erase (partial) annotations. E.g., when I write a large formula or drawing and screw up midway through, there's no way to erase part of what I wrote. I have to erase everything and start over. That's really annoying. -- one can't view a PDF annotated in this app with any other app, because it's hideously buried and spread out over multiple sudirectories of the "papers" directory. -- one can't click hyperlinks ,i.e., navigate to webpages shown in an PDF. WTF. -- The "Undo" and "Redo" buttons don't work. PDF Expert addresses most of these issues (and btw there is now an OS X app, but it costs extra $'s), but one problem at least with the iPad Pro is that it doesn't support muti-page view. The iPP is perfect for viewing two pages of a PDF document at once. PDF Expert is therefore suboptimal for the IPP (each book page is way too big). Any other apps people can recommend?