If you really have a company, your bookkeeper should teach you how to issue invoices.
If you don't have a company and want to fake an invoice, then paypal invoice won't fit, because technically it's not an invoice but rather just a payment order. I know that my clients from some countries say their bookkeepers and tax offices accept paypal invoices, but most of my clients say in their countries they can't do that. I can't do that either.
So just google for online invoice generator, there are plenty of them.
Important: that was neither legal nor bookkeeping advice, but mere technical one. The real advice is here: faking invoices is illegal in most countries. You might be traced, caught and punished.