Yes, this is imperative. Make sure the details on the form are identical to the one you submitted online (unless you need to correct an error). Either way, you need to check the ‘CORRECTED’ box at the top of the form to avoid duplication.
If you left the TIN box empty when filing online because you don’t have a Social Security Number, add your country’s equivalent on the hard copy (i.e. National Insurance number for the UK).
You must autograph your beneficiary name on the back of copy A. Do not remove the perforated edge on the left. Lift copy A using the right-hand edge to autograph the back of copy A. DO NOT autograph copy B or C. See the instructions here.