Adding read/write privileges to process

Hi,

I am working on an application which is a Windows Service.
There is another process which needs to be called from user context by my service. This I have achieved using Imporsonating logged in user token.
Everything works fine with user with Administrator rights. But local or limited account , in a case where I need to read from critical file, The imporsonated process fails because of limited privileges.

My Problem is
1. My Service needs to create a process which will run in logged in user context.
2. The new process should have privileges to read/write files (same as service)

I tried different ways to do this but in vein. I tried calling AdjustTokenPrivilges() but it didnt worked for me

Can anyone plz help me resolve this issue,

Thanks in advance.