Do you know the name / location of the folder?
Yes, the path would be something like filewin:/D:/JobInvoices/3898475_trucking_????.pdf
Does that help?
Okay, but the PDFs for each job are not stored in independent folders - they're all stored in the same folder together?
Yes, that's correct.
Drat. If you had a separate folder for each job, it'd be easy (Import from Folder would do the trick).
As it is, you'll probably have to use one of the plugins that allow file manipulation. ScriptMaster from 360Works should be able to do it. You can also use the BaseElements plugin, which is free, and I'm sure there are a couple of others out there that will allow you to manipulate the file system. Troi File comes to mind. Then you can set a variable and pull out all the documents that match the prefix you're looking for and just loop through them.
Another option, which may not suit given the workflow, would be to go ahead and pull them into FileMaker using container fields and then you can just use native FileMaker functionality to display them (Export Field Contents / Automatically Open File).
Edit: On second thought, Import from Folder probably wouldn't have worked anyway; I think it's restricted to images, now that I think about it (I'd have to double-check).
Second edit: It looks like the limitation on importing only images has been removed. According to the Integration Guide, any kind of file can be imported when importing files from a folder. (My curiosity overcame my laziness.)