How do I batch replace 100 different linked images in my AI file and export 100 different named PDFs?

Hi all!

This is driving me crazy...

So I have my A4 AI document with a QR code at the bottom (don't ask why I'm using QR codes, client work) and need to replace it and export the A4 poster as a PDF. I need to do this 100 times with 100 different QR codes and save 100 PDFs.

To summarise I need to,

1. Open A4 document (that has artwork already).
2. Drop in QR code A near the bottom.
3. Export as PDF A.

Repeat..

1. Open main document.
2. Drop in QR code B.
3. Export as PDF B.

And so on x100....

I have a experience with actions in Photoshop but not batch actions or scripts, and obviously need to run it in Illustrator...

Can anyone help?

Thank you!