.HDK File Extension
What is an HDK file?
File used by HotDocs, a document preparation program; contains a publisher key required to register templates for commercial use with the HotDocs Player; provided to the customer by a HotDocs sales representative after purchase.
When you receive an HDK file, you should copy it to the HotDocs program installation folder. After it is copied, new program options are available when publishing template sets.