Files with dfi file extension are associated with Digifont system. They include font description data.
DFI file extension - Digifont outline font description
What is dfi file? How to open dfi files?
File type specification:
The dfi file extension is related to Digifont.
The dfi file contains outline font description. Outline fonts (also called vector fonts) use Bézier curves, drawing instructions and mathematical formulas to describe each glyph, which make the character outlines scalable to any size.
This dfi file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.