Editing PDFs - why cant I copy and paste within a PDF and keep the font?

[Nicholas5FBB]

I have a PDF made on Windows, using News Gothic MT. I need to change a "2" to the word "two". I found the word "two" existing in the document and in News Gothic MT. When I paste over the "2" with "two" the font changes to Microsoft Sans Serif.
The preferences for Fallback font for editing is set to Let Acrobat Decide.
The file does have an edited subset of News Gothic in it.
What have I done wrong? I am working on a Mac in latest Creative Suite.

[Test Screen Name]

Do you have the News Gothic font liecnsed and installed on your mac? You cannot edit with fonts that are only embedded.