Document Conversion
DocViewer uses GroupDocs as its primary document conversion service and iWorks for Apple files. There are lists of supported file types and supported fonts. If a document fails GroupDocs, it will then be sent to the LibreOffice converter, unless it's an Apple file in that case it will converted by iWorks only.
There is a separate project that manages document conversion called KnightRider. KnightRider is used by DocViewer, but has its own repo and is listed separately on Gerrit. Knight Rider