I can't ask my dad anything anymore as he has Alzheimer's, but he had given me his book collection and I've been scanning them, too. (Of course I don't cut up the sentimental treasures, but there are only a handful of those.)
Also, years ago, he got low vision and couldn't read comfortably anymore. If it was today, I would set up a projector to throw the pdf pages on the wall so he could keep reading.
I buy the physical book, cut the back off, scan it to a pdf and throw the book into the recycling bin.
On the book scanning note though, do you have a special book scanner? I've never seen one outside of professional shops and turning the pages seems like a ginormous hassle.
I use a Fujitsu fi-5120C hopper-fed scanner (does both sides at once) and a QCM-8200M stack slicer. Those make short work of most books. The Fujitsu scanner software includes an OCR. I scan at 400dpi. If a page gets messed up, I use pdftk to merge in corrected scans.
I also use it to scan in small mountains of old tax records and documents I had stuffed everywhere.
The odd thing is I've come to prefer the pdf images, as they look like a book page (!). This works out great on ereaders with larger screens like the Kindle DX, or the Kobo Aura which has an HD eink display.
The regular Kindle is a bit squinty with a paperback sized PDF, but I bought some dimestore reading glasses which helps wit dat.
I welcome the advent of better and better ereaders.
The files go into my Box account, and I never lose another book.
This. I have a bookcase filled with "me". Those books constitute what molded me, and (if unread) what I hoped would. My longevity being in some doubt, my kids being very young, and my ability to tell them what's in my head limited, in large part I keep that bookcase filled and arranged in hopes that someday they will discover it, read the contents, and so absorb much of what their father is (or, at that future date, was).
E-books, while convenient, can be lost en masse in an instant. Heck, a bunch vanished last week from my tablet when I upgraded the operating system (most were recovered, but not all). My wife may be irritated at the space occupied by my paper books, yet therein is the point: they're not going away any time soon without real effort. Atoms persist; bits are fleeting.