In PLDA 5.2 "CDA4" button is hidden by default. It can be set to Show / Hide in the Page / Settings dialog.
CDA4 is an example of Special Application. It was created for a client that often imposes pages to be printed on CD stickers, that look like this:
Advantage of this option is more automatic imposition then simple Step-Repeat or N-up imposition. The sticker's center is counted and then the stickers are placed to the sheet thus eliminating size differences in PDF supplied by many clients.
If you need to scale the stickers before imposing, choose the scale and then click CDA4 again.
If you need to impose pages in a way that cannot be automatically applied by current software versions, please send your request to firstname.lastname@example.org.
Include detailed description of the imposition and also sample PDF files, if that is possible. We will contact you to inform you whether such an imposition is feasible (usually it is), the price and date when a special plug-in for you may be ready.