"Import Selected" button doesn't work in iMovie for some files
I use iMovie to edit videos a LOT, and some of those videos have a still shot .pdf that I import as an information screen at the beginning or end of a video. For a long time I could import those files to the project no problem, but a few months ago it stopped working. The file names are not greyed out, I can select the file for import, but when I click on "Import Selected" nothing happens. No error message pops up, the Import window does not close. The blue button shows that I am clicking on it, but literally nothing happens.
I have been able to get around this by copying and pasting that media from other events, but I would like to stop doing that as I worry that it creates tangles in the library reference data (be kind if that's a stupid thing to say...I'm just guessing).
The event I'm trying to import to is named and has other video files in it. I am able to import some .pdf files but not all of them. Again, the files that I want to import are NOT greyed out, and appear to be available just like the others I CAN import.
Help!?
MacBook Pro Retina