Is there any way to have xschem plot a schematic and all sub-circuits as one PDF?

It does have a print option, I believe you can print as pdf, png, or svg

Yes. I was using that. I do not see any way to get it to recursively print though. In other EDA software when you print a hierarchical schematic you can have it include all the subcircuits too

Looks like you can run it in batch mode with the

-p

option (see help). It should be relatively simple to write a script to print all the circuits in a directory (or hierarchy) and them merge them with a tool like PDFedit.

Xschem has a hierarchical ps/pdf export that does exactly that. It also adds links in the pdf so you can click a component and go to the corresponding schematic page