Installation guide for PRO PDF API


I have subscribed to PDF PRO API monthly tier, as i want to escape the pdf limit of pages and size. I have received 3 API endpoints and an API key.

1- I don’t know what to do next.
2- Where to put the API key?
3- How to upload my PDF and get them ocred?
4- If i have an online website (Vbulletin Forum), can i install a page for ocer there to be as a commercial service? and how?
5- Any guide to use on my desktop?
6- When I click the three links it gives me this message:

The requested resource does not support http method 'GET'.

I am very newbie but can follow Installation guide if available. Please need your help, I haven’t found steps for installation guide.

I am using Windows 10 Pro
My online web site server is Centos
I have very little knowledge with PHP