Not a valid archive? - newbie question

Folks,

Newbie here.... with hopefully a newbie question.

I'm running pg 7.2.3 on RedHat 8... so far with tremendous success.

I did a pg_dump of a fairly large DB sometime ago... and now i'm trying
to pg_restore it.

I get a reponse saying "does not appear to be a valid archive"

I can view the dump in a text editor.... it *seems* fine and intact.

Any suggestions?

Responses of RTFM are welcome if you reference an M and page number :-)

thanks,

-jspeer