QR Bar Code.
DisplayBarCode field.
Bar Code Add-In

Automatically number Word documents by Graham Mayor, MVP
If you use this it inserts a Content Control in the document. I also inserts a document variable. You can use that variable in the QR code.
The variable is varSerialNo.
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(If you use the macros rather than the Add-In, the variable name is "VarNum."

I've changed your question to remove the word "page" from it. The "page number" in Word parlance for your document would be "1."