> Do PDFs not treat the TAB character the same as the TAB key?
- No. They treat it as a part of the text, which it is.
> Is there another ASCII character than can be used to advance to the next fillable field in a PDF?
If you want to import data into multiple fields you should use the Import Data command (under Tools - Prepare Form - More). This will allow you to select a tab-delimited file, then a row from that file, and then it will import the data from that row to the matching fields (the field names have to appear in the first row of the file, of course).