I added a few PDFs to Calibre and put them in my e-reader to see if they rendered okay.
They did not.
I put the e-reader back in and in Calibre selected the PDFs and selected “Remove matching books from Device”.
This command permanently and without warning deletes the PDFs from your hard disk.
But it’s worse than that.
What I have now also found is that it does NOT remove them from your e-reader, and you now *cannot* remove them from your e-reader because Calibre will not show the ebooks because they are not in the Calibre library.
I mean, on one hand, I’ve known and always known Calibre was insane, because of it’s UI. This behavious is *not* out of keeping with how the program presents itself.