Read mpp file inside a document library with C#.NET

I have the following piece of code to open a project file in a SharePoint 2013 event receiver. 

ApplicationClass projectApp = new ApplicationClass();

                projectApp.FileOpen(filePath, true, Missing.Value, Missing.Value, Missing.Value,
    Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value,
    PjPoolOpen.pjDoNotOpenPool, Missing.Value, Missing.Value, Missing.Value, Missing.Value);

This read the file well when the variable file path is assigned with a local path. eg: (@"D:\\test.mpp")

But if I assign a SharePoint document library url where there is an actual document, it removes part of the url and say that file cannot be opened.

Its a COMException and the error is as follows.

{"The file \"//spapp/ProjectDocumentLibrary/test\" cannot be opened."}

The actual value of the fileName variable by the time this is executed includes the http part and the .mpp extension. 

Any thoughts on overcoming this?