Hi,
If it's just for your own use, you can add ?tmpl=component to the URL of your product page, click on the print button of your browser and in the print prompt, select "save a PDF" and you'll get a PDF of the product page content.
If you want something automatic, so that your users can click on a button to get a PDF version of the product page, I'm afraid it would require the development of a full plugin. While the plugin could potentially reuse the data already loaded on the product page, it will still require generating your own HTML and CSS for the PDF version as the HTML to PDF libraries out there cannot handle all the HTML tags and CSS commands you would have on a normal website page.
That's what we had to do for the PDF invoice plugin we have on our marketplace.