Hello
It is possible to create a process order without a BOM and you can manually input the materials or explode a BOM from a different material.
Please observe that this is a very simple scenario, which you can easily test on a test system. Before opening this kind of thread in the future, I suggest you to take a look on the blog Asking Good Questions in the SCN Discussion Spaces will help you get Good Answers, which explains what you must consider when asking a question on SCN.
BR
Caetano