PDF not searchable

Unfortunately it is not possible to search a PDF. Furthermore it is (mostly) not possible to mark text passages to copy it. “Mostly”, because occasionally a blue marked area appears a few lines above the mouse.
I’m not sure, but I mean to remember that this worked in the past. (Beta

PDFs are searchable and text can be copied, but obviously the PDF file must support it, i.e. must not be scanned/image like pages.

I have checked several PDFs once again: Sometimes the search works and sometimes not. This also applies to the same document: Once I can search it - the other time I can’t. It doesn’t seem to make a difference whether the PDFs are HTML converted PDFs or PDFs with additional (OCR) text layer.
It is not possible to mark text accurately in any case.