I need to invoke functions of the Microsoft Office Protector (OpcIrmProtector) from C#. This protector implements the I_IrmProtector interface (details: http://msdn.microsoft.com/en-us/library/ms475158%28v=office.14%29.aspx[^]). Calling HrInit() is no problem. But for e.g. HrIsProtected() I need to provide an implementation of ILockBytes. Has anybody experience how to correctly implement ILockBytes in managed code? I am a bit at a loss as to what is expected here. For unmanaged code I found a sample that uses CreateILockBytesOnHGlobal(). This returns an unmanaged instance of ILockBytes. Is there any chance of using this unmanaged instance from managed code (probably not...) or marshalling it into a managed structure? Or is there a similar method for C#? In that case I wouldn't have to implement ILockBytes, which would save me a lot of time. Of course, I could implement this part in unmanaged code, but I'd prefer a solution in managed code, if possible... Thank you!