Is there a way to take 2 letters and make them a ligature if there is not one built into the font.

Hello,

I am picking up an old job and need to use the old font with it. This particular font doesn't have a ligatures for when 2 ff's are next to each other and I need to make them into a ligature, Is there a shortcut that will do this in InDesign?

We had one in quark back in the day, but now using InDesign, I need to find something that will work here.

Thanks

babs