Symptoms

Opening some PDFs from smartform view connected to SharePoint library gets error Page cannot be displayed
 

Diagnoses

Doc libraries with large amounts of meta data ie columns increases the URL to over the 2000 character limit ie IE breaks at 2048 which causes 404 to be thrown.
 

Resolution

TFS 671645 ie 4611.25 flips the GET to POST hence alleviating the issue.