Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The ZPK file type is primarily associated with 'ShipRush' by Z-Firm.
ShipRush is a shipping solution, that connects directly to websites and programs to automate the shipping process. Compatible sources include Amazon, OpenCart, Outlook and even SQL Databases.
.ZPK files are template files used by ShipRush.