My internal Packing Slip is printed on a full sheet of copy paper, as well.
Never had a problem. As long as they can scan the Shipment ID barcode when it arrives.
I also print my USPS Shipping Labels, and tape this way.
The tape is clear, so it's easily scannable by ANY barcode scanner, and the tape somewhat protects the ink smearing (should the package get wet.)
Been doing it this way for years. No issues.