Above, I wrote that the permission has to be set to “editable” or “installable”, so I’m not sure why “preview/print”, which is a stricter level, should work. I’ll need to look into it some more.
– Is it recommended to use the purge command or rather not for best compatibility?
When you’re ready to distribute the PDF, yes, you should definitely use the Purge command to reduce the PDF file size. It makes no difference to compatibility.
You can do this with FormMagic by setting the text size to 12.345. More info: https://www.id-extras.com/help/formmagic/#:~:text=3.2%20%C2%A0%20%C2%A0The%20magic%20font%20size%3A%2012.345pt!