Abbie, much thanks for replying.
The Index Rules was one of the first things I checked (before submitting the initial query).
The settings, by default, and for all file types, were (already), and are (still) as you indicated in your last step.
However, as another check, I also ran searches, again with various search-term entries, after changing the Index Rule to:
“All ‘.pdf’ Files Will Be Included“.
Same result. ZERO file matches from the 15,000+ pdf files on the c:/ drive.
But it’s actually worse, and stranger, than that.
My initial focus was pdf files because that file format is by far what I have most of.
I have determined subsequently that the same problem occurs with virtually* all file formats, except EPUB documents, as follows:
With bare basic search terms such as “the” or “and“, Anytxt returns results for various (presumably ALL match-relevant) file formats on the E:/ drive (pdf, doc, docx, txt, ppt, pptx, xls, xlsx, xlsm, one – etc.).
However, it returns ZERO results from the C:/ drive for file formats – pdf, doc, docx, txt, ppt, pptx, xls, xlsx, xlsm, one – etc., WITH one notable exception. From the C:/ drive it returns results (hundreds, so again, presumably ALL match-relevant files) for EPUB documents.
(*There were also a trivial number of matches from txt files matched from the C:/ drive, those txt files all being AppData, not User-generated files.)