I have managed to use OVRDrop for the display of FSWidgets' GMapHD in AeroflyFS2 recently. This is using a WMR (Acer AH101) headset and does not required controllers (which I don't use).
Installation and arranging the 2D window for proper display was a bit tricky, but after this has been done once it's quite easy to load the saved setting and run it.
Unfortunately, OVRDrop does not come with a proper manual. However, the manual of OpenVRDesktopDisplayPortal being a precursor works quite well. You may even try to use the program OpenVRDesktopDisplyPortal at Github itself as a free alternative (which I didn't try, though).
This should be usable for pdf (and other 2D) display as well.
I tried a couple of alternatives at Steam but failed to get them to do what I wanted.
Kind regards, Michael
Edit: Thanks Phil, you were faster, so mine is one of the clunkier alternatives indeed.