I recently upgraded my project from .net 3.5 to 4.0. My Word Interop Assembly was working on client machines just fine in .net 3.5. After upgrading to .net 4.0 I changed the Embedded Interop Types property to false. Now some clients are looking for Interop.Microsoft.Office.Core when previously they weren't. My question is how come the clients are looking for this assembly with .net 4.0 when they weren't in .net 3.5?