PGP File as input is required for output, thats what you want to decrypt...its the purpose of the command
Taken from the guide:
The usage format is:
pgp --decrypt <input> [<input2> ...] [<inputd>...] [options]
Where:
<input> (required). Space-separated names of the files to decrypt.
<inputd>. Additional detached signature target files. Note that PGP Command
does not write output when decrypting detached signature files.
[options] modify the command.
If the the file is empty, encryption will be done and when decrypting, it will still be empty.
Please mark post as solution if questions addressed.