Hi,

There are no detailed instructions on advanced or specific export scenarios.
A lot of information can be learned from the related UI codefiles - in ~\CMSModules\ImportExport\Controls\ folder on the contrary.

Shortly said, in your code, you will need to modify the ObjectProcessType for the Documents object type for the export settings object. You want to set it to "None" for documents, which will be:

settings.SetObjectsProcessType(ProcesObjectEnum.None, PredefinedObjectType.DOCUMENT, true);

where settings are SiteExportSettings object.

Hope this will help.

Regards,
Zdenek