How to extract 2 first and 2 lats pages from acrobt document with variable x-pages using java and than save it with the same name as the pdf +_cover?

It's a bit tricky because these are two separate ranges of pages, so they can't be extract to a new file directly.

You would need to create a new document and then append those pages to it, delete the original blank page it has, and then save it.

Most of these tasks will require a script to be installed no the local machine, or the code will have to be executed from the JS Console.