.KTH File Extension

Presentation theme file used by Keynote, an Apple iWork program used to create presentations; contains the default graphics, fonts, and layout settings for a presentation; used for saving presentation templates.

To open a Keynote theme, select File → Choose Theme... from the application menu, or select a theme from the Theme Chooser when the application starts. You can save custom themes by selecting File → Save Theme....

Custom KTH theme files are saved to the following directory by default:
[user]/Library/Application Support/iWork/Keynote/Themes/.