Thanks – not a stupid question at all! That was my first thought, but I was able to select text in Preview. On the other hand, I’ve now opened it in NitroPDF, and that was unable to find an OCR layer (or at least offered to create one); and conversion to text (thanks for that suggestion, which I hadn’t thought of!) failed. So I think Preview must have been applying Vision to make the text selectable. Normally Play Books purchases come with a text layer, but I couldn’t swear that that’s always been the case, and it does look as though what’s happening here is that the PDF came without one and DT has labelled it as PDF+Text because Vision can process it.
If that’s the case, it would be great if there was a way to distinguish between an imported/indexed PDF with an existing text layer and one dependent on Vision for (reduced) searchability. But so far this is a one-off, so I’m not sure I’ve decisively nailed what’s going on here.
