I had a word doc, on a PC, which I wanted to put into iBooks on my iPad. I converted it to a PDF, on the windows laptop, and imported into File Browser, so that I could then open in iBooks. Ios11 no longer seems to have Open In, but now has Share File, so I shared it with iBooks and the PDF openned up. When I closed it, in iBooks for later reading, the PDF was not listed with all my other books and PDFs. I tried this several times to no avail, until, in iBooks, I tried the icon of the square box with an up arrow- I am not sure what the proper name is for it- and found Copy to iBooks as a menu item. This did the copy I wanted, but it took a while to find it and seemed counter- intuitive. Btw, on my iPhone 8, sharing the file, again from File Browser, did what I expected it to do and copied the file straight into iBooks. (While I used File Browser above, I see this more to do with ios 11 and iBooks.) Perhaps this is described somewhere, but if not the above may help someone else.