I currently have thousands of images that have been uploaded to my computer and organized using Canon's ZoomBrowser EX. These images have keywords entered via ZoomBrowser. I'm wanting to start using Lightroom instead to organize all my images. Will the keywords be copied over to Lightroom or will I have to re-enter all the keywords when I switch over to using Lightroom?
Are the keywords visible in any other program or in Explorer/Finder? Are they written to the files? Which file types?
If yes, there is a chance they will. If not, I doubt.
There's only one way to find out. Install the test version or post an image on a file sharing service so we can test for you.
ZoomBrowser has long been notorious for locking up keywords and captions in its proprietary database, inaccessible to other software. At least as of several years ago, ZoomBrowser didn't provide any means to save keywords and captions in industry-standard metadata fields inside the photos, so that they could be read by other programs like LR.
I did a quick search, and it appears that is still the case. I did find this free utility for saving the keywords and captions to the photos' metadata: ZB Meta Save - Browse Files at SourceForge.net I have no idea about the quality of the utility. I strongly advise that you verify your backups are actually working before invoking it.
If it works, then once you've saved the keywords to the photos using the utility, LR will read them when you import the photos.