You can ignore this question because I already found a solution. At imposition module I used a Page Order: "Job Group", at Rows and Columns I choose "Assymetric Rows and Columns". At Layout Style I choose "Guilhotin Cut".
Good night! I have a client that needs to send a PDF file with several several pages, being that each page of that same PDF file can be a different size. He wants to impose this entire file so that it is optimized for printing and does not have to create a new flow for each PDF he receives, as each file received can have different page formats. I saw that there are third party software that do this (they call it ganging and I just have to indicate the size of the physical printer page that the software is in charge of optimizing the layout of the pages for the best use of the paper). The need is for use with digital printers and also for flows with offset printers. Is it possible to do this with the FreeFlow Core imposition module?