Index/Synchronize not including files

I have a folder on my computer (just call it “Top”). In this folder are several levels of subfolder, with several files at the bottom level (PDFs, primarily). When I tell Devonthink to index Top (via File -> Index), it creates the folder hierarchy correctly, but none of the regular files get indexed (no files appear in Devonthink). Choosing “Synchronize” from the File menu does not accomplish anything. For testing purposes, I also created a text file in Top, and that doesn’t appear in Devonthink either when I synchronize.

I was under the impression that synchronizing an index folder would cause all files beneath it to appear in Devonthink as indexed files. If that’s what’s supposed to happen, what’s going wrong?

I have Devonthink Pro Office version 2.0.6.

Oh, one more thing.

There is a soft link to the folder in question in my Dropbox folder, so the folder is being synced over Dropbox. However, I am indexing/synchronizing the original folder, not the symbolic link. Should that matter?