globetrot,

Use the OutputTo method of the DoCmd object to generate an RTF and name it according to the desired invoice number. Then automate Word to send it to whatever PDF printer you have that retains the file name when it creates the PDF. I use Adobe Acrobat for this, and I have a routine that waits for it to show up in the specified directory (Adobe outputs only to one directory), and then moves the file to the desired location on my file system.

I also tend to favor Word over Access's Report tools, since converting from Access Reports to RTF can lose elements like graphics. That's the point of view, anyway, for my response to your question. A non-exporting alternative would be to build a little routine to wait for a generically named PDF to appear in the file system, and then rename it in accordance with the invoice number.

HTH!