SP 2013: Posting Documents to Library using SP List Web Services

The scenario: there is an external system (php backoffice) which will post documents with their metadata to SharePoint Site (library).

I have SP Site which contains two Document Libraries:

1. Laws (which has columns: client, name, date)
2. Books (columns: author, publisher)

How can i use the SP 2013 WebServices to add Documets to a specific library with the necessary values for the columns.

For sure, we will not add the webservice as a webrefernce, we should pass the parameters through url, because the back office is php site isn't it?

Please, advice, and provide any tutorial?