.UDC File Extension

File used by InDesign, a desktop publishing and page design application; contains a word list used by the software's spell checker; can store exceptions and user-defined words, as well as words from a dictionary.

InDesign dictionaries can be accessed by selecting Edit → Preferences → Dictionary in Windows or InDesign → Preferences → Dictionary in Mac OS X. UDC files are often used to share custom dictionaries between multiple users in a company.