Unfortunately, each computer in the world represents data with its own format. The followings are end of lines used in major OSes.
As you know, if there is no agreement for end of line, text is not transfered between these OSes safely. RFC822 defines to transform end of line into CRLF. This kind of format conversion is called canonicalization. Converting SJIS and EUC-Japan to JUNET code is a kind of canonicalization.
OK, let's think about encryption and signature with PGP. Suppose that a Mac user signed text whose line breaks are CR then sent it to a UNIX user. If the UNIX user transforms line break to LF then verifies the signature, it is obvious that the verification fails. You thus understand that canonicalization is necessary.
When you encrypt or sign text with PGP, first convert it to ISO-2022-JP then transform its end of lines into CRLF.