What is the CRF file format?
A .crf file is a proprietary game resource archive used by the Enhanced Dark Engine, developed by Looking Glass Studios and Irrational Games. It packages game assets - level maps, textures, audio, and 3D models - into a single binary container for runtime loading.
Games using this format include Thief: The Dark Project (1998), Thief II: The Metal Age (2000), and System Shock 2 (1999). The archive begins with the four-byte ASCII signature fknc (hex 66 6B 6E 63), followed by a file table listing the names, sizes, and byte offsets of embedded assets, then the raw asset data.
The format was reverse-engineered by the modding community; no official specification was published. Dragon UnPACKer 5.x is the primary extraction tool. Modders creating custom fan missions for these games package their content as .crf archives.
All three games are available on GOG.com and remain actively maintained by community patches (TFix for Thief 1, T2Fix for Thief 2, and the NewDark engine updates). .crf serves a similar purpose to the .pak archives used by other game engines of the same era.
Security & safety
RISK: LOWCRF files are internal game data containers and cannot execute code on their own. They are safe to open in Dragon UnPACKer. As with any game mod content downloaded from the internet, be cautious about the source - ensure you download CRF files only from reputable modding communities.
Format details
in a nutshell- Cardiac Risk File (medical) - Some medical software uses .crf for cardiac risk assessment data - completely unrelated binary format.
Programs that open CRF files
Windows3 apps
Dragon UnPACKer
Free File > Open, select the CRF file, browse the file list, and use Convert/Extract to save assets. 
ZipZag
Free Legacy tool; may open some CRF archives, but development is abandoned - prefer Dragon UnPACKer. 
Thief: The Dark Project / Thief II / System Shock 2
Paid The games themselves read their own CRF archives at runtime; you do not open CRFs directly in-game. Technical details
deep spec| Magic bytes (offset 0) | 66 6B 6E 63 (ASCII: fknc) |
| Byte order | Little-endian |
| Encoding | Binary (proprietary; no public specification) |
| File table | Header contains embedded asset names, byte offsets, and sizes for all entries |
| Asset types | Level maps, textures, audio files, 3D models, AI scripts, game data |
| Compression | Varies per asset entry; engine-specific or uncompressed depending on asset type |
| Typical file size | 5 MB - 500 MB |
| Platform | Windows |
| Games using format | Thief: The Dark Project (1998), Thief II: The Metal Age (2000), System Shock 2 (1999) |
| Engine | Enhanced Dark Engine (Looking Glass Studios / Irrational Games) |
| Primary extraction tool | Dragon UnPACKer 5.x |
| Modding use | Custom fan missions packaged and distributed as .crf archives |
| Specification source | Reverse-engineered by modding community; no official documentation exists |
| Released | 1998 (System Shock 2 / Thief: The Dark Project era) |
| Latest version | Enhanced Dark Engine (no formal version numbering) |
CRF conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about CRF files.
