Most of the rules I have are in PDF and prefer them in that form to read them. I am not too bad in finding stuff in them (via a 2-in-1 Windows machine). but I always create a (or less often use the supplied) one or 2 page very useful QRS that I always print out. The only exception to the printed QRS is Armati – I have a QRS but know the rules quite well and so do not use it anymore. A very useful QRS is so handy so long at is has most of the stuff and rules lookups become rare. I could probably look at it on a tablet butt find the one page so easy to use and it is only printing a page or two.
Oh, and there was once I did have to print out some of the rules (Crusader Ancient rules) as it was easier to read one of the sections (I think on Skirmishing) and cross reference that with other parts of the rules – one of the few times just having a PDF made it difficult – even having it open twice just did not cut it 🙁
It may help that in my day job I am very paper-lite. I have a laptop and read and write everything on that. I cannot remember the last time I printed off anything to read (maybe 2013?) and the only time I write something is to sign a form.