We've got a similar situation, and used this:
Options$="FILE=<Filename>.pdf"
Open (Chan,opt=Options$,err=Oops)Wdx$+"*PDF*;View"
.
Print(Chan)...
.
Close(Chan)
As long as you include the ".pdf" in there, it should be fine. Also, since WDX$ is used for opening *PDF*, you don't need it on the filename.