Missing 3.55GB of PDFs in Books app on iPad

Can’t see ALL pdfs accounting for 3.55 gig shown under ipad setting> ipad storage>Books> 3.55G.

Even when uploading many pds to idrive and then deleting them ( after downloading to usb) , the count of gig on Books keeps increasing .

Where are all my pdfs going and keep using data space? Why can’t i see them?

I have researched and tried i tunes but that doesn’t show them and it doesn’t even have a pdf option for file type, only audiobooks.

I tried Apple support and we got cut off after about ten min and they just said contact us back if you need us!! Why didn’t they offer to send me a solution on info already discussed?

I am going crazy. Can anyone please advise me.

[Re-Titled by Moderator]