There is only one file type that uses the .UDC extension:
Adobe InDesign User Dictionary
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 selectingin Windows or in Mac OS X. UDC files are often used to share custom dictionaries between multiple users in a company.
Updated: July 11, 2018