There are 4 file types use the .VDF file extension:
1. Gothic Game Data File
Data file used by the Gothic video game series; contains worlds, characters, 3D models, textures, and sounds; Gothic II VDF files are stored in the /Gothic II/Data folder.
VDF files may be edited with GoMan or a hex-editor, but typically should not be altered. Incorrectly modifying VDF files may make them unusable.
Updated: February 26, 2009
2. Valve Data File
A VDF file is a data file format used by Valve's Source game engine. It contains various kinds of game metadata, including data for resources, installation scripts, configuration scripts, and visualization elements.
VDF files can often be seen when installing games distributed through Valve's Steam game client, such as Half-Life 2 and Counter-Strike. The file features Valve's KeyValues format, which is a plain text format that saves key-value parameters in a tree hierarchy. The format is similar to JSON and YAML. While VDF files are meant to be used by the Valve Source game engine, you can open the files with a text editor to view the contents.
NOTE: You can view more information about Valve's KeyValues format on the KeyValues Wiki Page.
Updated: November 24, 2017
3. VirtualDub Video Filter
Filter plugin for VirtualDub, a video capture and processing utility program for Windows; adds extra features such as special effects and additional file support to the VirtualDub program.
VDF filters can be loaded into VirtualDub by clicking on the "Load" button in the Add Filters dialog box. They will be loaded automatically if the VDF files are placed in the plugins folder within the VirtualDub program folder.
Updated: March 29, 2007
4. AntiVir Virus Definitions File
Data file used by AntiVir, an antivirus application for Windows; saves virus definitions, which contain signatures that are used for recognizing viruses on the computer system; often downloaded during software updates so the software can check for new viruses.
VDF files are saved to the AntiVir installation directory and have the filenames vbase000.vdf, vbase001.vdf, etc.
Updated: October 1, 2011