Files that contain the .thmx file extension are most commonly associated with theme files that have been created for 2007 and later versions of a variety of Microsoft Office applications. The THMX files that are used by these programs contain themes that a user can apply to a document or to a presentation that has been created by the associated software.
THMX files often contain pre-defined colors, formatting and fonts and can be used as a template that lets a user create multiple files with a similar look, but without recreating the settings for each file. THMX files are similar to application template files, but unlike application template files they can be shared across multiple Microsoft Office applications.
For example, a THMX file can be used in both PowerPoint and Word instead of having to create a template for both applications.
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If you have additional information about the THMX file format or software that uses files with the THMX suffix, please do get in touch - we would love hearing from you.