How to display pdf from other drives in an iframe?

Question

i tried displaying pdf tat is inside application path and it works. But i need to display pdf from other drives how do i do it?
this is my code:

string filepath = Session["path1"].ToString();
System.Web.UI.AttributeCollection aCol = iFrame1.Attributes;
aCol.Add("src", filepath);
where i get path from a database and i also tried server.mappath and bt got error of using physical path
help me..