When i run in Notepad++ its giving me error Xrm is undefined

function Page__onload() {

 }  

if( Xrm.Page.getAttribute("new_project").getValue()!=null)

{     

Xrm.Page.getAttribute("new_proj").setValue(Xrm.Page.getAttribute ("new_project").getValue()); 

}  

function ProjectNumber() 

{     

if( Xrm.Page.getAttribute("new_projectnumber").getValue()!=null) 

    {    

 Xrm.Page.getAttribute("new_projnum").setValue(Xrm.Page.getAttribute("new_projectnumber").getValue().toString());

}      

else

{      

   return error;    

 } 

}