In first edition, there was a home-grown postscript interpreter, psi, but it was replaced by gs in second edition. The degree of difficulty depends upon what `it' is. gs can interpret and emit Postscript or PDF of varying versions, and includes a substantial set of Postscript fonts. As I recall, just getting a Postscript interpreter to render reasonably quickly (er, less than pessimally slowly) is quite a job. PDF seems to be an attempt to rein in the full generality of the Postscript language.
Perhaps the people who make Forth interpreters could make a fast Postscript interpreter, though I suspect that graphics is the bottleneck.
