Adobe recommends that driver writers do not put EOT (control-D) into files when saving to disk. Normally, the EOT is a part of the protocol for parallel and serial ports and never hits the PostScript interpreter.
Drivers that do embed EOD can create problems for devices that allow other communication methods (e.g. AppleTalk, Ethernet, and SCSI) where the EOT is not part of the communications protocol. It is useful to redefine EOT in these instances so that the interpreter does not generate an error. The recommended redefinition is:
(\004) cvn {} def
This should convert any stand-alone embedded EOTs into a null procedure. This definition does not cause all 004 characters to be consumed, it just prevents an "undefined" error if you try to execute one.