In order to make use of the functionality that is provided by external DLLs from within your form script, you need to add a reference to the DLLs. The default behavior when adding a reference is to embed the referenced file within the form template when it is generated. This ensures that the DLLs are in place and available on the client machines when the form templates are downloaded.
However, when you are referencing Mi-Forms DLLs such as the DatapathExportModule.dll file, you do not need to embed the DLL since it will already be present on the client machine as part of the standard Mi-Forms Client installation. Not embedding the DLLs will help to keep from increasing the size of the form template wwhich will result in faster performance when synchronizing with the Mi-Forms Server.