Hello,
Sorry to say but it wouldn’t be directly possible as you know the default Single Product page layout comes from WooCommerce end.
But you can try the mentioned change using the Theme’s Layout Builder to create Custom Layouts for the Single Product page > and in that Layout you can add a button related to PDF Download. You can find the Layouts under the Dashboard > Layouts.
As you will have different Download Links, then you can make multiple Layouts on your Site under the Dashboard > Layouts and can make them appear on specific Product Categories products using the Conditions option available.
Here is the Guide to that: https://xtemos.com/docs-topic/single-product-page-builder/
Further, you can read more about the Layout Builder here:
https://xtemos.com/docs-topic/woodmart-woocommerce-layout-builder/
Hope this helps !
Best Regards