Document Conversion and Versioning

When you choose a converter to use on a specific version of a document, Microsoft SharePoint Server 2010 examines the document library to determine whether there is already a converted copy of that document generated using the selected document converter. If there is, SharePoint Server 2010 ends the conversion.
This rule applies to a specific version of the original document. If you change the version number of a document, either as a major or minor version change, SharePoint Server 2010 considers it a new original document in terms of generating converted copies. You can generate new converted copies of the new version using the same document converters you used on previous versions.

For example, suppose you have a document, whose version number is 1.0, in a document library that has a single document converter available. You select that converter, and it creates a converted copy of your document. If you try and create another copy of that same document using the same converter, SharePoint Server 2010 stops the conversion because a converted copy already exists in that document library. However, suppose you make revisions to the document, and increment the version number to 2.0. You can now select that same document converter, and SharePoint Server 2010 allows it to generate a new converted copy, with a version number of 2.0. The previous converted copy, with a version number of 1.0, remains unaltered in the document library; however, it has no relationship to the new converted copy, or the 2.0 version of the original document.
The following figure shows this relationship. Each converted copy is generated by a single document converter, from a single original document. If you change the version number of the original file, you can generate new converted copies using the same document converters again.