Simple postscript question

[Joel Hammer]

Total newbie on postscript, but:

I am trying to edit some pdf files (35, actually) off the net.
They converted easily enuf to ps with acroread (to see the command line
options, acroread -help).  I have gotten them cleaned up,(Just gotta
love sed.) but am puzzled by the show command they use.

Here is how they redefine show in these documents:
 /Tj { Show } 1 !
 I think they are redfining show, but I don't see a def operator. Oh well.
To print a string, they use this sort of command:

(MACROSCOPIC \(check all that apply\)) Tj 

Could someone explain what the /Tj {Show} 1 !
 line is saying? Especially, what the heck do the 1 and ! do? I would
really like to know since I want to insert some text into these documents
and it would nice to know what Tj does. If I try it, I get a stack error
or somethin'.

(BTW, once they are edited, they convert nicely back to pdf with ps2pdf.)

Thanks,
Joel