PDF embedding: 2023 edition

 Solely for my own benefit, some updates to how to create PDFs from Latex/Overleaf that meet the PDF/A standard required by various publishers, whose own instructions miss out several important features. 

• The final missing piece: make sure that hyperref receives the pdfa option.  In particular, if you are using acmclass call it with
  

  \documentclass[pdfa]{acmart}

  Or similar adaptation, e.g., \documentclass[sigconf, nonacm, pdfa]{acmart}.  Yes, I'm looking at you, PVLDB. 

•  Throw in 
  

  \usepackage[a-2b]{pdfx}

  I've no idea if this does anything useful, but why not?

• Edit 2025 edition: check to see if there are any Type3 fonts snuck in because these are bad bad bad apparently.  One egregious source of type three fonts is using the \mathbb{}font.  Instead \usepackage{dsfontt} and replace with \mathds{}. Thanks to the good folks of stackexchange for this tip.  

•  Go back to your plots in python, and make sure that Matplotlib is instructed to not use type 3 fonts.  The correct answer is of course 42, as in 
  

  import matplotlib
  matplotlib.rcParams['pdf.fonttype'] = 42
  matplotlib.rcParams['ps.fonttype'] = 42
  

  or something similar. 
• If all else fails, give up and run it through https://tools.pdf24.org/en/pdf-to-pdfa 

Hopefully that will do it.  Web services like https://avepdf.com/pdfa-validation can be useful at debugging things, if you don't mind uploading your documents to a random server, and running out of free goes.