How to add missing fonts to Adobe Illustrator?

Question

When opening an Adobe Acrobat PDF document on Mac OS X Lion to edit in Adobe Illustrator CS6, I got the message:> The font Helvetica-Narrow-Bold is missing. Affected text will be displayed using a substitute font.The font QuickTypePi is missing. Affected text will be displayed using a substitute font.How can I provide the missing fonts so that no substitution occurs and upon return to Adobe Acrobat Pro X the original fonts will remain after any edits in Illustrator?Or, since the message talks about their display, will the font remain unchanged upon return to Adobe Acrobat?

Answer 1

1. Get free fonts from DaFont.
2. Search using the font name the error is showing.
3. After finding the font download. 
4. The font file you select is in a .ttf format.
5. Just double click on the .ttf file and install it.
6. last thing restart your Illustrator.