I am sorry for the experience you suffered with Adobe Tech Support (although I am not part of Adobe Tech Support), but I think I can give you some assistance.
When you edit text in Acrobat, in order to maintain the look of the document in terms of the font originally used, you must have that font installed on your system. What likely happened was that when you edited the PDF on your Windows system, the font used by the text being edited was actually also installed on your system, but when you went to the MacOS system, that font was not installed. If you can install the font(s) on your MacOS system, does the problem go away?
If you don't have the font installed, we can't edit with it. This is both a practical and legal issue!
?I don't have the font/typeface on my PC either.
Why can Nitro PDF edit perfectly a document on my PC?
Why can't Adobe do the same on my Mac?
Then, when you need assistance with Adobe, you end up speaking to
some third world person who can't speak English and who is in no hurry
to help you. Again, I am not getting paid to call Adobe but the Adobe
service people are getting paid. I am told they will escalate the problem
and have somebody else call me and no one calls me.
Adobe is a rip-off.
If you don't have the font installed on your system and the program (whether it is from Adobe or Nitro) and assuming that the font is subset-embedded in your document, the following is true:
(1) Practically speaking, there isn't enough font information from the embedded font to fully and properly format any added or replaced text unless the font is fully-embedded OpenType font (not just not all the glyphs, but all the other OpenType tables). Very few PDF files have fonts so-embedded.
(2) If you try inserting a character that is outside of the complement of glyphs defined in that font subset, you would be either out of luck or a character would need to be synthesized from a substitute font.
(3) There are severe legal issues associated with how you use fonts that are already embedded in a PDF file. Generally speaking, you cannot legally use those fonts for editing or forms use within the PDF file unless the font has its flags set for either editable embedding or installable embedding. Most fonts do not have such liberal licensing terms.
As such, if you try editing text in a PDF file that has a font that isn't installed on your system, we (nor Foxit) can legally do such edits. We do what the legal system (whether we like it or not) mandates we do in this regard. I can't speak for Nitro. If they are letting you edit with an embedded font, they are at best on shaky legal grounds and also may put you in a situation where certain characters may not be available for editing, a double-whammy!
Obviously, if you are trying to edit text for which the font is neither embedded in the PDF file nor installed on your system, no vendor can “perfectly edit” your PDF file.