The indexer is set up to search pdf file contents. There are no other apparent indexing or searching problems.
This looks just like the problem that existed in previous versions of Windows. Attempts at using new Adobe iFilters / jFilters or by running registry hacks were claimed by some to have fixed things but others reported no change.
The only wholely reliable solution at the time was running two searches
1 using Windows explorer in case the content was in a non-pdf file &
2 using Adobe Reader Advanced search function in case the content was in a pdf file.
Is this limitation affecting all Windows 10 installations or just mine?
Is there a well-tested solution other than just installing Adobe Reader & using its Advanced search function again?