Option [Split & merge] becomes available when your document contains marked pages.
[None]
The document is printed on one printer.
[Split]
The printer only prints the sheets with marked pages. For example, you have marked all colour pages in the document. If one side of a sheet is a colour page, then the complete sheet is printed on a colour printer. The percentage of sheets with marked pages is shown.
When you select option [Split], the document is printed without any finishing settings.
[Merge]
This setting will print your document and insert the marked sheets at the right place in the document.
When you select option [Split] or [Merge] you can select:
[Use separate paper trays]
Select this option to allocate a separate paper tray for each type of insert sheet.
So, if you have five different insert sheets in your document, you need at least six paper trays. One paper tray for the normal paper and five paper trays for the insert pages.
If you do not select this option the different insert sheets must be put in one paper tray. So, if you have two different insert sheets, than put the insert sheets cyclic (1-2, 1-2, ...) in one paper tray.