I can’t delete a pdf from Books

I use iBooks to store pdfs when I need them offline. They may need instructions for the car stereo or guides for houses we’re staying in from Airbnb. I usually get the pdfs from an Email.

when I’ve finished using the pdfs I’d like to remove them but some I can’t.

On my iOS device I go to library / edit and then select the items however there is no option to select the items I want to delete (old train tickets etc). Here is a screenshot. Any ideas?