Windows 7 x64
Acrobat Standard 8.1.5
firefox or IE or right click in shell and select convert to PDF
invalid command sometimes is xshow
%%[ ProductName: Distiller ]%%
(varies) not found, using Courier.
%%[ Error: invalidfont; OffendingCommand: show ]%%
%%[ Flushing: rest of job (to end-of-file) will be ignored ]%%
%%[ Warning: PostScript error. No PDF file produced. ] %%
OK, are you using IE or Firefox? The steps you are using are not clear. If it is a web site you are looking at, what is the URL so others can see if there is an issue? The error simply says it can not find the font mentioned and is using Courier instead. This is not uncommon and may just mean that your system does not have the font used on the site (like Helvetica or such). You may be able to select in the job options to create the PDF even if there is an issue with the font embedding. As I said, knowing what you are looking at would help a lot.
I am surprised you got this far with AA8 in Win7. It is nice to know what seems to work with the new OS. You might want to update. AA8 is currently at AA8.1.7.