A very useful facility In Nitro is the option to append pages that are created with PDF creator. By saving it to an existing file name you are asked if you want to append or overwrite. Very handy, saves many clicks. Good thinking Nitro!
Alas, if I scan a bunch of stuff to PDF, extract a page in Nitro, or download a PDF from elsewhere, and try to save it in the same way to an existing document, I am not given the append option. Can't see any good reason why not - the sub-routines are already there.
I scan everything - paperless office. Append would be really handy. Also for my Grandson for compiling a "dossier" from scanned pages to cheat on his homework.
Of course I know about the combine and insert options - my arthritic fingers can't handle the multiple clicks require to perform these feats of endurance - open the target file, save the extraction, perform the insertion, go back and delete the extracted file...