Troubleshooting fonts is among my least favorite Mac tasks. Understanding precisely what is going on and what fix is needed too often seems a bit above my pay grade. Case in point: I recently launched Font Book for the first time since upgrading to Snow Leopard (Mac OS X 10.6). I was surprised to find 16 "duplicate font" warnings. These had not been present when I had last opened Font Bonk in Leopard (Mac OS X 10.5).
Now, as I see it, duplicate fonts are not necessarily much of a problem. Actually, if they truly are exact duplicates of the same font, they should be no problem at all--other than the waste of drive space. Where a problem can occur is if the duplicates are variations of the same font, perhaps in different font formats or created by different font designers. Even here, there are reasons you might want to retain both versions. (Read this PDF of an Extensis article for more on this point). However, especially if you work on documents where minor differences in fonts can have a significant effect on page layouts, you may have a clear preference for one of a duplicate pair. In such cases, you'll want to deactivate the undesired duplicate.
If I had not launched Font Book, I would probably have never discovered the duplicates and would have continued in my blissful ignorance. But now that I knew about them, I felt obligated to address the matter.
After some investigating, I discovered the single source of all of the duplicates: One font of each pair had been installed as part of Microsoft Office (and was located in /Library/Fonts/Microsoft); the other had been installed by Snow Leopard and was in the /Library/Fonts folder. That's why the duplicates didn't show up until after I had upgraded to Mac OS X 10.6.
For no particular reason, other than that the Snow Leopard versions were newer and from Apple, I decided to deactivate the Microsoft versions of the fonts. This turned out to be a bit easier said than done.
Font Book does include a Resolve Duplicates command. Using it, I could select all the relevant fonts and deactivate one of each pair of the duplicates in one step. Unfortunately, this command gives you no control over which version of the font is deactivated. Font Book decides on its own. In my case, Font Book decided to deactivate the Snow Leopard versions--the opposite of my preference.
I tried another font utility, FontDoctor. It had similar problems. Actually, it alerted me to even more duplicates, because FontDoctor checks the /Library/Application Support/Adobe/Fonts folder, which Font Book does not. I decided to ignore these for now. I had enough on my plate with the Microsoft duplicates.
Rather than continuing a search for a better utility, I shifted to a more blunt object assault: I removed the entire Microsoft folder from my Fonts folder. Sure, I was removing numerous unique fonts as well as the duplicates. But I had looked over the list and none of the fonts were ones that I used or needed. Or so I naively thought.
It turns out that Microsoft uses some of these fonts all on its own. I became aware of this on my next visit to Microsoft Word's Style menu. The names of many of the styles were now an unintelligible string of symbols. This was because Word wanted to display the names in the now missing Eurostile font. When it could not find Eurostile, it shifted to "Type Embellishments One LET" instead.
So much for the blunt object assault. I returned the Microsoft folder to the Fonts folder and relaunched Font Book. I selected Show Font Info from the Preview menu. After selecting each duplicate font, I checked the Location line to determine which version it was. If it was the Microsoft version, I deactivated it (using the Disable command in the Edit menu). It was a bit tedious but, so far, this has worked without any negative side effects. Now about those Adobe font duplicates...
This story, "Bugs & Fixes: Font Duplicate Misadventures" was originally published by Macworld.