[sovre]

5th wiggle, thanks for your reply. Before returning to the forum, I actually ended up reaching the same conclusion you posted here as a result of tireless experimentation!

In case anyone else encounters this problem with a file containing text they want to be able to copy, highlight, etc. I also discovered a solution.

Here is what I did:

I loaded my image-based file into ABBYY Finereader. I then saved another version of the file, after selecting "text under page image" in Finereader's PDF options.

Result: I now have a file with which I can use dictionary/copy/highlight, and although the text contains some sections with non-roman characters, changing to "text under page image" did not result in a loss of or distortion of any information in the text, so far as I can see.