Are Acrobat pdf files a legally accepted way of transmitting purchase orders?

Are Acrobat pdf files a legally accepted way of transmitting purchase orders?
Because PDF files are more difficult to convert to allow users of make changes most companies readily accept these when dealing with transactions. Indeed in many MD(GP) surgery's the use of a letter from consultants in often copied toPDF and attached to a patients electronic file for ease speed and of course space saving. It is always wise to check with the person who is to receive these that they accept them in business. You could also follow up with a a hard copy if its required.