We are in need of converting all MS Office documents to PDF, TIFF, or any similar image format with no loss in formatting (these are official documents that cannot have tampering).
Is there any way to do this without installing Office on the machine that would do this? Ideally, this would go on a server and run multi-threaded without the overhead of Office Automation.
You could use a third-party library such as Aspose.NET for document conversion, but I'm afraid - if high-fidelity rendering is critical - there is no way around using the original application.
Microsoft Office provides a converter API which allows conversions without Office being installed. However, not only might you be facing license issues (IANAL), this API only supports conversions of text-processing formats that don't require rendering the document (e.g. RTF -> DOC, DOC -> DOCX), so it is not really an option for you.
Update: Probably the best option would be to have a look at the SharePoint 2010 conversion engine, which is exactly made for automated (server-side) document conversions. It's quite heavy though (both hardware and pricing) so maybe it is overkill for your use-case.