So I have about 50 PDFs in one folder (that I created, and with no security settings), and I need to combine them into a single multi-page PDF. Then I need to take a single PDF from another folder, and put it between each of the 50 pages from the first folder. I've done this a hundred times with many PDFs before, so please presume that this is not foreign to me, and I have become quite accustomed to the convenient act of dragging and dropping to specifically order and rearrange multi-page PDFs without using the "combine files in acrobat" wizard.
My Surface Pro 3 got caught in a BSOD loop recently, and required me to restore Windows 10 and reinstall all my apps. I am using Acrobat XI, as I have for a while. Everything else seems to be working fine since the restore, except for some reason I can no longer drag and drop PDFs from Windows straight into Acrobat. This is the exact same version I used a couple weeks ago without flaw, so I don't expect an update suddenly removed this functionality.
I open a PDF and extend the thumbnails pane. Then I attempt to drag another PDF from Windows explorer into the thumbnail pane, and instead of getting the little bar on either side of the existing thumbnail, to denote whether I want to place the new page before or after the existing one, I just get a black circle with a line through it. Dragging PDFs into the thumbnail pane is, for some reason, completely impossible. Again, neither of these PDFs have any security restrictions. Yes I am the administrator, running Acrobat as the administrator. Yes, I am familiar with the "combine files" feature, yet not only am I not interested in using it, but when I choose that option, I have the same black circle preventing dragging and dropping into THAT window. The files are on my computer, not the cloud or gmail or anything else. I have tried many different PDFs, including multi-page files I previously created using this exact method, and the problem persists. In multi-page PDFs, I still have the ability to drag the thumbnails around WITHIN the PDF, but I'm unable to drag new PDFs into the combined file. THAT is the issue.
I have scoured these forums and others for answers to the problem, and can't find anything. If you know why this is happening, and which setting I can change to re-enable dragging and dropping, I would love to hear it.