A .mht file is corrupted after you upload the .mht file to an Office SharePoint Server 2007 document library (Microsoft Support)
Consider the following scenario: You upload a .mht file to a Microsoft Office SharePoint Server 2007 document library. You create a custom column in that document library. You edit the values of both the Title and the Custom column properties. In this scenario, the .mht file is corrupted.
Filed Under: SharePoint General
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