[Edit: there is a suggested solution to the issue now at the end] The Surface Pro 4 that I am using is a versatile device and particularly strong in reading and commenting digital documents. I am regularly working on articles, seminar essays, thesis manuscripts and book lenght work, and it is really nice to be able to type text quickly like with a regular laptop, then flip the device over and start reading in full screen mode. When the PDF document is open, it is really handy to do the highlighting and scribble the review comments in the margins with the Surface Pen. However, the software does not currently support this fully. Adobe Reader Touch and Acrobat XI Pro that I am using both can be used with the Pen, but only to a limited manner, and through rather complex function selections. The best support for the Pen is built into the Microsoft OneNote, but there is one serious issue currently: when you open a PDF file in OneNote 2016 for editing (New Page > Insert > PDF Printout), a longer file will take literally hours to process. OneNote makes some kind of image file from each page and each letter, and does this very very slowly. This is simply not feasible. I have read that the older, 2013 version worked fast – I wonder what has gone wrong with the new, updated OneNote?
Edit (27 July, 2016): Marjolein Hoekstra from the OneNote Central (@OneNoteC) kindly reached out to me via Twitter and suggested a solution for the jamming PDF import issue – one needs to go to File > Options > Advanced, then look for Printout options group (at the very bottom of the list), disable the first option about printing to multiple pages, and then click ok/save the settings. This indeed appears to make the PDF import work for me, so: many thanks for the tip! Surface Pro 4 still struggles a bit to keep long, 300+ page PDF documents visible (rendering of the typefaces jams occasionally), but this is now at least a working solution.