This answer can only be given when further information is provided, for example, after the physical and virtual hardware and operating system. Furthermore we need statements about the complexity and size of the generated documents (MBytes, number of pages), in relation to their frequency. The specification documents/day can be too imprecise if there are peak times when not 4000/8 = 500 documents per hour have to be processed, but more. Please provide us with information on the peak load in "Documents per hour", with the corresponding size specifications of the documents.