Foxit Quick PDF Library Lite is an ActiveX and so does not require an Instance ID. The Instance ID is only required by the DLL edition of the commercial version of Foxit Quick PDF Library.
In addition, you do not need to — indeed, you cannot — call the UnlockKey function when using Quick PDF Library Lite because it is a free product and there is no license key required.
Register the ActiveX edition using regsvr32 on the machine(s) that you will be using the library on for development and deployment:
regsvr32 "DebenuPDFLibraryLite1312.dll"