If you have more than one company code, you might want to define a new document type and number range to differentiate between the two company.
Define a new number range not in used
OMH6 - Number Ranges for Purchasing Documents
Copy the NB - Standard PO to e.g. ZB
OMEC - Define Document types
Text for Document Header/Item
Text for Document Supplement
OMF6 - Messages Header Texts