Can we combine SAP PM with the normal project management methodology to attain maximum efficiency ?

Great Sajid. You are skillful PM. 

Yes, it can improve efficiency of overall project control... Now the concept of SAP PM is much elaborated to SAP EAM:

From Plant Maintenance to Enterprise Asset Management.

For Projects, managing assets and resources, knowing their utility at a particular point of time , with a proper tools is none the less important than the project activity. SAP PM/EAM provides an excellent platform for the same. Combining this resource details to a flexible Project Management Methodology can provide better results. 

Many thanks for the question, Mr. Muhammad Usman Tariq

off course we combine and it works efficiently to the project