The purchase order PDF is built from blocks you can switch on or off, so a supplier sees exactly what you want them to see - and nothing you would rather keep in-house. The switches live in Settings > Documents & email under PDF options; the letterhead, logo and standing note are covered in Customize the purchase order PDF.
A Currency row prints only when the order is in a currency other than your store's own, so a single-currency store never sees it. It rides the costs switch, since a currency code on a document carrying no money says nothing.
Whole blocks of the document can be turned on or off:
Show costs and totals - turned off, the document carries no money at all: no unit costs, discounts, line amounts, charges, tax or total. Useful when the PDF doubles as a picking or packing document. With costs on, the totals block also states Total units - the piece count across every line, net of anything cancelled - so whoever receives the delivery can check it against one number.
Show SKU column, Show discount column, Show pack breakdown, Show notes, Show logo, and Show account number.
Show payment terms - the Terms row in the block of dates at the top, which prints the terms saved on the supplier. On to start with, because it has always printed. Turn it off for one supplier, or for everyone, when your terms are something you track rather than something you want stated on their copy. A supplier with no terms recorded never prints the row either way.
Show supplier order number and Show customer order number - the two numbers you can record on the order itself. Both are off to start with, because most stores keep them for their own use: a number you typed for the warehouse should not reach your supplier unless you say so. With one switched on, the row still only prints when you have actually filled the field in.
Product images - a thumbnail beside each item, so a warehouse picking from your order can see what they are pulling. Off by default, and it adds to the size of the emailed PDF.
Variant column - prints the variant in a column of its own instead of after the product name. Off by default, and it hides itself when nothing on the order has a variant worth naming.
Barcode column - prints each item's barcode in a column of its own, for a supplier who picks or receives by scanning. Off by default, and it hides itself when nothing on the order has a barcode. The code printed is the item's current barcode, so one you add in Shopify after building the order still reaches the supplier.
Retail price column - prints each item's current selling price in a column of its own, so staff can price arriving stock straight off the printed order. Off by default, and it hides itself when nothing on the order has a price. The price printed is always the item's price in Shopify at print time, not what it was when the order was built.
Stock on hand - prints each item's current available stock at the order's location in a Stock column beside Qty, so staff working the delivery know what is already on the shelf and what goes to the floor. Off by default. When the order names no location it prints the whole store's stock, a custom line prints a dash, and the column stays away when no line has a stock figure. Like the other blocks it can be set per supplier and in the print dialog - remember it is on the supplier's copy too.
Bin location column - prints each item's bin location in a column of its own, so staff can put arriving stock away straight off the printed order. Off by default, and it hides itself when nothing on the order has a bin. Each line prints the bin for the location it is going to - on an order split across locations, every line shows its own warehouse's shelf. Set bins on the product page or by CSV - see Bin locations: record where each item is shelved.
Show our own SKU - when an item has a supplier part number, the SKU column prints theirs first with yours in small text underneath. Turn this off to print only the supplier's code. Clearer when you buy the same item from several suppliers, where your own code means nothing to any of them.
Vary them for one supplier, or for one send
These apply to every supplier. To vary them for one, open the supplier's page and use Customize for this supplier on the PO document card - turn a block off there and it's left off their copy only.
You can also change them at the moment you send or print. The Email to supplier dialog shows the whole list under The PDF includes, and Print or Download PDF opens the same switches as PDF options, already set the way this supplier's document is configured, and a change you make there is remembered for that supplier - so the second order to them starts where the first one ended. A choice that matches your store defaults leaves the supplier following those defaults, so a later change in Settings still reaches them.
Received status
One switch in PDF options is just for you: once anything on the order has been received, Show received status adds Received and Remaining columns beside the quantity - print the order and check the delivery against it, or file a copy showing exactly what is still due. It applies to that one print or download only: it is never remembered for the supplier, and an emailed document never includes it.