@Sandesh Mainali , All Azure Web Apps (as well as Mobile App/Services, WebJobs and Functions) run in a secure environment called a sandbox.
Each app runs inside its own sandbox, isolating its execution from other instances on the same machine as well as providing an additional degree of security and privacy which would otherwise not be available.
Windows Servers have a bunch of COM servers configured and available for consumption by default; however the sandbox prevents access to all out-of-proc COM
servers. like ADO (ActiveX Data Objects)/ a sandboxed app cannot call into WMI, or into MSIServer.
I see that you have a SO thread on this-as Charles mentioned 'Using Microsoft.Office.Interop.Excel.dll depends on the server to install Office software.'