"No PDFs" in iBooks on ipad; i.e. PDFs don't persist in Library

PDFs instantly disappear in iBooks after I click out of them.

In particular, I can read PDFs by going into the "Files" app, going to my icloud drive, clicking a pdf, then clicking "open in ibooks". The pdf shows up fine and I can read it.

However, as soon as I click the "back" button on the upper left corner of ibooks, in the "Library/PDFs" of ibooks, I see the book I just read appear for half a second, and then instantly disappear, and then it says

No PDFs. All the PDFs in your library will automatically be added to this collection.

What's going on? How can I get my Library -> PDFs screen in ibooks to actually show the PDFs that I have been reading, instead of having them instantly disappear? Currently, in order to read the PDF again, I have to go to the Files app, and click "open in ibooks" every time.

I'm using ibooks on ipad air 2, with the latest system upgrades as of late August 2020.

Solution 1:

By default, PDFs don't persist in the Books app. In the Files app, opening a PDF with Books will make the Books app open the PDF from its existing location.

To copy the PDF into the Books app, with the book open in the Books app, tap the Share button, then ‘Copy to Books’. This will duplicate the PDF into the Books app container.