Adobe Illustrator Artwork (AI) is a proprietary file format developed by Adobe Systems for representing single-page vector-based drawings in either the EPS or PDF formats. The .ai filename extension is used by Adobe Illustrator. The AI file format was originally a native format called PGF. PDF compatibility is achieved by embedding a complete copy of the PGF data within the saved PDF format file. This format is not related to .pgf using the same name Progressive Graphics Format. The same “dual path” approach as for PGF is used when saving EPS-compatible files in recent versions of Illustrator. Early versions of the AI file format are true EPS files with a restricted, compact syntax, with additional semantics represented by Illustrator-specific DSC comments that conform to DSC's Open Structuring Conventions.
In its first versions, the CDR file format was a completely proprietary file format primarily used for vector graphic drawings and developed by Corel Corporation, recognizable by the first two bytes of the file being "WL". Starting with Corel Draw 3, the file format changed to a Resource Interchange File Format (RIFF) envelope, recognizable by the first four bytes of the file being "RIFF", and a "CDR*vrsn" in bytes 9 to 15, with the asterisk "*" being in early versions just a blank, and beginning with Corel Draw 4, the version number of the writing program in hexadecimal ("4" meaning version 4, "D" meaning version 14). The actual data chunk of the RIFF remains a Corel proprietary format.