Note that there have been instances of Anti-Virus programs blocking Windows' File Associations. Disabling or uninstalling the Anti-Virus program may resolve problems setting File Associations.
1. Open the Windows Control Panel by clicking on the Windows button and typing in: Control Panel.
2. Select View By: Small or Large icon
3. Click Default Programs
4. Click Associate a file type of protocol with a program.
5. Click Choose default apps by file type.
6. Wait for the list to load and find the file type you would like to open (example .ofm, .dst, .exp), click on the app on the right and choose DesignShop.