Field operatives commonly mark-up printed paper copies of engineering documents (e.g. P&IDs) to identify modifications or errors of the as-built situation. These mark-ups (aka redlines) are an important record that are used to update the original document.
The paper copy is scanned and then linked to the original document.
If the printed copy had a unique identifier (e.g. QR code or barcode) then the system could use this to automatically identify the correct original document that is relates to.