When a batch gets created documents should get separated automatically without using separator sheet or Barcode separator.
How can I classify documents for Invoice and supporting document. In our project we get many invoices with supporting document so the scanning person has to insert the separator sheets manually, so to avoid this we want to automatically classify the supporting documents.
In general the concept would be that you would enable separation in the project and then train your classes with examples to be used for the layout or content classifiers.
However, as I'm sure you've seen, the obstacle with invoices is that they are different enough between vendors that it would not reliably classify all to an Invoice class. Similarly with "Supporting Documents" which are likely to be very different from each other, so unfortunately there isn't a completely easy answer without separator sheets (or barcode stickers affixed to supporting docs).
What you might want to do is write code in the one of the separation events like Document_AfterSeparate event. Despite the name, the document has not yet been split at this point, but the classifiers have run. See Scripting Help topic "Server Script Events Sequence > Document Separation > Standard Document Separation" for more detail. Setting the SplitPage property on the CDocPage (pXDoc.CDoc.Pages.ItemByIndex(lPage).SplitPage) will allow you to use your own logic to determine which pages to separate.
For example if you know that you will always have single page invoices, you can split on the first page and classify accordingly. Or you can try to search for something that indicates the end of the invoice like "Total" or other characteristics. There is an example of how you can use locators to help separation in the Scripting Help topic "Script Samples > Use Locator Results for Standard Document Separation". The example uses a Barcode Locator, but the same concept works if you wanted to try it with a Format Locator or anything else.