Yes, and alongside formatting challenges, PDFs commonly only include the glyphs from the font that are actually used in the document.
So if you had PDF with "Hello World" on it, you could feasibly change it to "Hello Hello", but wouldn't be able to change it to "Goodbye World" (as the glyphs for "G", "b", "y", and "e" are not included in the PDF)
Sure, you could do a bit of detective work to figure out which font it was from the glyphs or something and lookup and insert new glyphs into the PDF, but I can't imagine a generic PDF editor being capable of doing this for you.
Some editors get around this but just straight up switching the font(s) for the whole PDF, so they'll look different after saving.
So if you had PDF with "Hello World" on it, you could feasibly change it to "Hello Hello", but wouldn't be able to change it to "Goodbye World" (as the glyphs for "G", "b", "y", and "e" are not included in the PDF)
Sure, you could do a bit of detective work to figure out which font it was from the glyphs or something and lookup and insert new glyphs into the PDF, but I can't imagine a generic PDF editor being capable of doing this for you.
Some editors get around this but just straight up switching the font(s) for the whole PDF, so they'll look different after saving.