Type: Metafile
    Extension: WMF
      Version: 
  Compression: None
  Color Depth:
   Maintainer: Microsoft Corporation
Specification:

WMF is the native vector file format for the Microsoft Windows operating
environment. WMF files are actually a collection of GDI (Graphics Device
Interface) function calls also native to the Windows environment. When a WMF
file is "played back" (typically using the Windows PlayMetaFile() function)
the graphics is rendered. WMF files are device-independant and have no limit
to their size.

Most books on Microsoft Windows programming contain sections on the internals
of WMF files. The closest thing Microsoft has for a specification for the WMF
format is in Volume 4 of the Microsoft Windows Software Development Kit
Programmer's Reference. Chapter 3 details the internals of the Metafile
Format.

The Microsoft Knowledge Base (available at ftp://ftp.microsoft.com/kb/ and on the
Microsoft Developer Network CD) also contains the complete specification of
WMF. I also highly recommend the book:

  Inside Windows File Formats, Tom Swan, Sams Publishing 1993.
  ISBN 0-672-30338-8 $24.95 softcover, 337 pages.

The placeable metafile format was created by Aldus Corp. to allow the 
positioning of a Windows metafile on a printed page. These metafiles have
a 22-byte header then must be stripped before they can be used by the
Windows API. Have a look at the following Microsoft Knowledge Base article:

  http://www.microsoft.com/Softlib/MSLFILES/METAFILE.EXE
  This archive contains the METAFILE.HLP help file that describes
  the WMF file format.

  http://www.microsoft.com/Softlib/MSLFILES/PLAYMETA.EXE
  This archive contains sample Windows code to manipulate WMF files.

  http://www.microsoft.com/developr/MSDN/OctCD/METAFI.ZIP
  This archive contains the METAFI.HLP help file that describes
  the WMF file format. 

Also have a look at:

  http://www.r2m.com/windev/
    Internet Resources for Windows Developers