You can install an extension DLL by modifying the Windows registry directly, although you have to be careful with the naming of the registry keys.
To install a Win32 extension DLL, add a string value HKLM\Software\DobySoft\SoftCopy\ExtDllPath in the Windows registry. The string value should be the full path to the extension DLL eg. C:\Program Files\SoftCopy\extension\Release\softcopyex.dll.
To install an ActiveX or .NET extension DLL, add a string value HKLM\Software\DobySoft\SoftCopy\ExtComServer in the Windows registry. The string value should be the name of the COM server eg. softcopyex.main. The DLL must first be registered as a COM server through either the GUI configuration tool or the command prompt.
To check if the extension DLL is working, simply submit a sample print job to SoftCopy. If the output file is produced immediately, then the extension DLL is working correctly. If the "Save as" dialog box continues to pop up, then you need to recheck either the extension DLL or the installation.
Tip: If you write your own extension DLL and it is not working, try installing the sample extension DLL instead. This will narrow the problem down to either the extension DLL or the SoftCopy printer driver.
Note that registry entries are relative to HKEY_LOCAL_MACHINE because the extension DLL runs in the context of the print spooler (SPOOLSV.EXE), which executes under the local system account. This means the extension DLL does not have access to HKEY_CURRENT_USER, which is only available to processes running under the account of the active user. Hence, all registry entries used by the extension DLL must be located under HKEY_LOCAL_MACHINE.