Font Embedding

Tools> Print Production> Preflight> Fixups.

You can include the preflight in an action, using the Action Wizard tool, where you can apply the action to single file or a folder of files. It might be a good idea to address the issue of why the fonts are not being properly embedded in the first place.

Do you own an actual copy of Helvetica? It is not easy to get the actual font file needed today, as the world has moved on to OTF fonts.

Converting to PDF/A should be done only if you actually need PDF/A files. It causes major inconvenience to make them when not needed, e.g. if changes are needed later.  You should be able to embed fonts (if you have them) using preflight, including applying to a small batch. (Acrobat is NOT a tool for medium or large scale automation work, that way lies limitless pain...)