AC File

What are AC files and how to open them

Are you having problems opening an AC file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your AC files.

What is an AC file?

AC files have multiple uses, and AC3D Geometry/model is one of them. Read more about the other uses further down the page.

AC3D Geometry/model

AC3D Geometry/model files (extension .ac) store 3D models in plain text form for use in the AC3D modelling program by Inivis. They capture complete mesh-based appearance data such as the arrangement of surfaces (polygons, outlines, lines), material attributes, paths to textures, and UV mappings. Designers working on scenery, virtual environments or simulation visuals save their work in this format.

These files are authored using AC3D, where users build 3D objects by composing surfaces into objects, assigning materials, and linking texture images. The .ac files are then editable by AC3D and can be imported by other modelling tools through plug-ins or scripts. This format is commonly used for scenery or object models in simulators such as FlightGear and in scenery design workflows for X-Plane (models may be exported from .ac to X-Plane's .obj format).

The file content begins with the ASCII signature "AC3D" followed by definitions of objects, surfaces, vertices and polygons. It is human-readable, enabling manual editing of texture references, surface settings and geometry. It contains the keywords OBJECT and POLY, among others, to mark different structural sections.

How to open AC files

We have identified one AC opener that is compatible with this specific type of AC file.

Programs that open AC3D Geometry/model files

Last updated: August 5, 2026

All known file formats using extension .AC

While AC3D Geometry/model is a popular type of AC-file, we know of 2 different uses of the .AC file extension. Different software may use files with the same extension for different types of data.

Ancestral Quest Family Tree Database

The Ancestral Quest Collaboration Database format with extension .AC is a special type of database used by Ancestral Quest when sharing or working jointly on genealogy files. It is generated by Ancestral Quest only when the user employs the Collaboration (NetFam) feature; the usual format for ordinary single-user databases is .AQ. Ancestral Quest writes .AC files to allow multiple users to open, edit, and synchronize the same family database.

An .AC file contains all the genealogical data typical of an Ancestral Quest database including personal records, family relationships, sources, notes, events, and attachments (photos, audio, video). Because it serves collaboration, it supports concurrent access, tracking, and merging changes by different users across systems or platforms. The .AC format is read and modified only by versions of Ancestral Quest that support Collaboration, and when upgrading to newer versions (especially v16), collaborative files may require conversion so that all collaborators use compatible versions.

In technical detail, .AC files begin with the byte signature "CAQ" followed by a null byte (hex 43 41 51 00) at offset zero.

AC opener for Windows

We have identified one AC opener that is compatible with this specific type of AC file.

Various apps that use files with this extension

These apps are known to open certain types of AC files. Remember, different programs may use AC files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about AC file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.