Acrobat Professional is the right tool to hammer your screw.
Converting PDFs to JPEG isn’t exactly editing. You can typically use any online converter to convert a PDF to a JPEG or PNG.
As @PrintDriver alludes to - it’s not the best option for online where text is considered. The text is converted to an image - and that means for online it’s no longer searchable, which could be an issue.
And sending out large emails by Constant Contact wouldn’t be wise either as they might not accept large emails being sent out and it could hit a lot of spam filters and reduce your target audiences by not receiving them - or you could end up being blocked altogether.
All in all - Affinity Publisher is a good option - as you can open PDFs directly and make edits etc and export to whatever format you need.
It’s not entirely clear what your goals are - I don’t really get what you’re trying to do.