How to change font size or use another font in Quick Look on OSX?

You will not be able to change the size of the font directly in the pop up (discussed here), but you can change the size of the pop up box to make the text larger and easier to ready. @Howie in an answer to a Super User question did a great job at explaining how to do this:

From Ars Technica Forum, courtesy of username DarylF2:

link to Ars Technica Forum

I figured it out, and is was actually pretty simple.

Show the package contents for "/Library/QuickLook/iWork.qlgenerator/" and edit "/Library/QuickLook/iWork.qlgenerator/Contents/Info.plist".

Change the "QLPreviewHeight" parameter value from "600" to your new value (I used "1000") and change the "QLPreviewWidth" parameter value from "800" to your new value (I used"1333").

That's it.

I didn't need to reboot or even log out and log back in for this to take effect, but I did need to open a few Pages document Quick Look previews before it seem to "take".

As always, back up the original file first and realize you are editing a file Apple didn't intend for the end user to edit.

I just tested it and it works for iWork documents only. PDF and other types of previews aren't affected. I'll try to see if there is more to it than that.