DDT File

What are DDT files and how to open them

Are you having problems opening a DDT 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 DDT files.

What is a DDT file?

A .DDT file is a Diagram Designer Template file.

Diagram Designer Template files store collections of reusable shapes, symbols, or objects that can be inserted into diagrams built with the Diagram Designer program by MeeSoft. Templates help users keep frequently used objects - flowchart elements, shapes or even library icons - ready for quick drag-and-drop into new or existing diagrams. They are particularly useful when creating diagrams with recurring components, symbols, or standardized sets of objects.

Diagram Designer itself creates and uses template files. Users can build a template palette by collecting objects - either drawn directly in the program, imported from metafiles or bitmap images, or pasted in - and then saving the palette as a template file. That template file, when loaded, populates the program's template pane, making its contents available for further diagrams. Templates remain editable: users can copy template objects into diagrams, convert layers into new palettes, or save modified palettes under new template files.

These template files are binary files written by Diagram Designer. They are identified by a byte signature at the start of the file consisting of the hexadecimal bytes 03 44 44 74 (".DDt" in ASCII) at offset zero.

How to open DDT files

Important: Different programs may use files with the DDT file extension for different purposes, so unless you are sure which format your DDT file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested three different DDT openers which you will find listed below.

Last updated: October 22, 2026

Various apps that use files with this extension

These apps are known to open certain types of DDT files. Remember, different programs may use DDT 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 DDT file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.