I had a need today to try and figure out exactly what the auto-margins for PDFs were. What I mean by this, is the actual margin size on the output document when you have your template set to 0 margins.
I tested this on a “Letter” sized PDF. Before today I was under the impression that the auto-margins were the same no matter what size output file you selected, but I did not test that. I will most likely do more testing later, and will post my results.
I found that the left-side margin was 0.08 inches,
and the top margin was 0.34 inches.