Actor Character Table (file format)

Actor Character Table

Screenshot of Rover's ACT loaded in Microsoft Bob.
Name	Actor Character Table
Extension	.ACT
Initial release	March 10th, 1995 (30 years ago)
Operating system	Microsoft Windows, Classic Mac OS
Successor	Agent Character Storage

An Actor Character Table (ACT) (also known as an Actor Character File) is a legacy file format used by Microsoft Actor, the predecessor to Microsoft Agent. ACT files store the full character data for Microsoft Actor characters, including their artwork, sound files, and associated metadata.

Actor Character Table files are generated upon a successful compile of a .UCH file, which is the Microsoft Actor equivalent of Microsoft Agent character's .ACD file. If the .UCH is in a valid format, the Utopia Animation Editor will parse the .UCH through WRITEACT.DLL to generate an .ACT file.

Unlike character files used by Microsoft Agent, .ACT were only known to be utilized in a couple of Microsoft software releases:

• Microsoft Bob (Microsoft Actor 1.0)
• Microsoft Bob 2.0 (Microsoft Actor 2.0, unreleased)
• Microsoft Greetings Workshop (Microsoft Actor 2.0)
• Microsoft Office 97 (Microsoft Actor 2.0)
• Microsoft Greetings Workshop 2.0 (Microsoft Actor 2.0)
• Microsoft Office 98 (Microsoft Actor 2.0, Classic Mac OS version)
• Microsoft Office 2001 (Microsoft Actor 2.0, Classic Mac OS version)

Version differences

Although both Microsoft Bob and Microsoft Office 97 used the .ACT extension, the internal structure of Actor files compiled for Microsoft Actor 1.0 and Microsoft Actor 2.0 differs significantly between the two. Microsoft Actor 2.0 files have a larger header structure compared to Microsoft Actor 1.0 characters and a drastically different internal structure if a Bitmap image is used. In addition, while Microsoft Actor 1.0 files are supported by Microsoft Actor 2.0 programs, the same is not true vice-versa, mirroring the behavior seen with Microsoft Agent 1.5 files being supported by Microsoft Agent 2.0 programs but not vice-versa.

Version differences

Aspect	Actor 1.0 (Bob / Rover.act)	Actor 2.0 (Office 97 / Clippit.act)
File extension	.ACT	.ACT
Header size	24-bytes	26-bytes
Version (offset 0x002)	01 00 (1.00)	02 00 (2.00)
Color table support	Unsupported?	Yes, example: 0060: ...FF FF FF 00 (White) 00 00 00 00 (Black) C0 C0 C0 00 (Gray)
Image format	Windows metafile (.WMF) & Bitmap (.BMP)	Windows metafile (.WMF) & Bitmap (.BMP)
Natively supports	Microsoft Bob only, can run on Actor 2.0 programs	Microsoft Bob 2.0, Microsoft Greetings Workshop 1.0 & 2.0, Microsoft Office 97, 98, 2001, can only run on Actor 2.0 programs

Image format

Unlike Microsoft Agent character files which utilize 256-color Bitmaps or GIF files, Microsoft Actor Character files primarily use the Windows metafile (WMF) image format, a 16-bit format introduced in the 1990s with the release of Windows 3.0. Generally, most Microsoft Actor files contain at least 200 WMF files, which contain the individual eyes, mouths, and other assets the characters consist of.

Microsoft Actor 2.0 files have extra space in the header for a color palette, allowing for Microsoft Actor characters to have a custom palette defined if BMP files were utilized instead of WMF.

WMF frames of Clippit converted into PNG.

Trivia

• Little documentation exists for Microsoft Actor or the .ACT format, as Microsoft Agent succeeded Microsoft Actor within two years of its release.
• Unlike its successor, Microsoft Actor uses .WMF images instead of .BMP/.GIF files.
  • Despite this, the Microsoft Agent Character Editor has built in .WMF support that is not officially mentioned in any public documentation.
  • Theoretically, Microsoft Actor could support 24-bit color as WMF is not restricted to 256 colors.
• As of 2026, there are only 29 known Microsoft Actors files.
• Microsoft Actor 2.0 is the only virtual assistant technology by Microsoft to be available on a platform other than Windows, with Office 98 and Office 2001 for Macintosh using Microsoft Actor assistants.
• All Microsoft Actors for Office 98 and 2001 for Macintosh are Microsoft Actor 2.0 characters, as indicated by the version header: 00 02
  • However, the Mac version uses a different image format than .WMF files, which is currently unknown.
• Microsoft Actor files are supported on Windows 3.1 or later, a version earlier than Microsoft Agent files which are supported by Windows 95 or later. In addition, Microsoft Actor files are supported by Mac OS 7.5 through Mac OS X Tiger 10.4.11.