I'm testing GoldenDict 1.0.1-289-g0da4b83 with Windows 7. It works correctly with Word, Notepad etc. I tried it with the same PDFs in several PDF readers. As usual, GD's Scan Popup fails to detect anything when I merely hover the cursor over a word in the PDF; that is not a bug. As usual, Goldendict notices and translates the word in the PDF when I click on the word and either click Copy or use Control-C; that is not a bug either.
However, in Adobe Reader X (10.1.4), an error message appears in response to the Copy/Control-C: "There was an error while copying to the clipboard. An internal error occurred." This does not happen when I do the same thing with the same word in the same file in any of the other PDF viewers.
Turning off the Scan Popup feature in GD immediately stops the problem in Adobe Reader: i.e. neither the Copy command nor Control-C causes a problem. Switching GD's Scan Popup feature back on immediately starts the problem again.
I conclude from this that something in GD is causing a problem in Adobe Reader, but not in any of the other PDF readers that I tested. The problem doesn't appear to be fatal (I just click on the error message and it goes away), and it doesn't prevent GD from working, but it needs to be looked at.
Best wishes,
Alec.