page_format isn't working for me.
Your page "Put a 'Save as PDF' link on your website" has a link to download the page as A4. That doesn't happen when I click on it. Instead I get something that's about the size of my browser window (I'm guessing).
I think this is broken.
Thanks for the feedback, but the page_size parameter does work. It could be that your default reader settings make the PDF appear smaller.
If you open the PDF in Adobe reader you can double check the page size by going to File and then Properties.... (CTRL+D) and you will notice that it's indeed A4.
Please feel free to sign up for a free trial and try all kinds of page sizes - http://pdfmyurl.com/request-trial