Windows Metafile (WMF) is an image file format originally designed for Microsoft Windows in the 1990s. Windows Metafiles are intended to be portable between applications and may contain both vector graphics and bitmap components. It acts in a similar manner to SVG files.
Essentially, a WMF file stores a list of function calls that have to be issued to the Windows Graphics Device Interface (GDI) layer to display an image on screen. Since some GDI functions accept pointers to callback functions for error handling, a WMF file may erroneously include executable code.
WMF is a 16-bit format introduced in Windows 3.0. It is the native vector format for Microsoft Office applications such as Word, PowerPoint, and Publisher. As of 2017 revision 14 of the Windows Metafile Format specification is available for online reading or download as PDF.
In 1993, the 32-bit version of Win32/GDI introduced the Enhanced Metafile (EMF), a newer version with additional commands. EMF is also used as a graphics language for printer drivers. Microsoft recommends that “Windows-format” (WMF) functions only “rarely” be used and “enhanced-format” (EMF) functions be used instead.
With the release of Windows XP, the Enhanced Metafile Format Plus Extensions (EMF+) format was introduced. EMF+ provides a way to serialize calls to the GDI+ API in the same way that WMF/EMF stores calls to GDI.
There are also compressed versions of Windows Metafiles known as Compressed Windows Metafile (WMZ) and Compressed Windows Enhanced Metafile (EMZ), which are basically gzip compressed WMF and EMF files correspondingly.