For security reasons, file that is uploaded into form is scanned and also a check for its identity is carried out. Cellosign process does not take the file extension for example “.txt” that was uploaded for granted but rather check that the file signature (“identity”) and calculate the output file extension. In some cases a file could be uploaded as “.txt”, “.pdf” for example but the archived document could be “.bin”. That is because the file carries binary identity, mostly octet-stream identity.

OK, so what do I do next? Since this file cannot go through Cellosign with the original extension contact your client to get the file in other mean.