Microsoft's OneDrive is a very credible alternative to Google Drive or Dropbox, and today it's getting even better, albeit in beta format. PDF editing support is now included, a very welcome addition, as well as a notification view to see who's commented or edited a file that has been shared with you.
The PDF annotation works very well - I was able to highlight, strikethrough, draw a textbox, comment, and scribble on a document with ease. The delete edit function can be a little finicky due to the fact that editing precise details on a touchscreen is hard, but once you've got the hang of it, there'll be no trouble. Colours can be changed and textboxes can be moved around or resized, although there's no typeface or text size changes at the moment. When the editing is finished, a new document is saved, so the original document, sans edits, is still available.
Left: Previous version of OneDrive, with no PDF annotations. Right: PDF annotations on a document, showing a strikethrough.
The notifications feature works as expected. Someone shares a document, a notification pops up showing this. Nothing to write home about, but it's there - something else for Microsoft to tick off the list.
This is a beta APK, so either join the Google+ Community for OneDrive Preview, then register as a tester, or download the APK from APK Mirror. Keep in mind, though - if you download the APK you will not get future beta updates.