What does the page with folded corner mean?
A Folded Corner:
A shortcut icon has a folded corner, so it's most likely a shortcut you created, somehow, using “Save As...”.
What does the folded paper icon mean printer?
You'll also see this in physical printers, where an extended fold (revealing the lines indicating content) instructs a user which side with the content should be inserted into the printer feed: Ideally pair an icon with a text label if possible.