But perhaps the answers to my questions will help you too!

From the samples I've tested (less than 1% of the total number of files)
they all seem to be small. less than 10 sheets, file  sizes less than 100kb.

the 'tab-AD' string will appear multiple times throughout the document.
these documents seem to be pseudo-forms.
That is, they seem to be tabular, but without the tables. merely tab delimited.