Here's a nice curl example of the api:
curl -F "htmlFile=@test.html" -F "width=8.5" -F "height=11" -X POST -H "Content-Type: multipart/form-data" -o result.pdf http://thisurl/

OR

curl -F "url=http://www.google.com" -F "width=8.5" -F "height=11" -X POST -H "Content-Type: multipart/form-data" -o result.pdf http://thisurl/