Posting Pdf to chatter via bulk api?

Question

Which object should we use to post data's to chatter?I am trying to post a pdf file to a chatter object using curl.

What is the name of the object that we should specify in txt file?

<?xml version="1.0"encoding="UTF-8"?>
<jobInfo xmlns="http://www.force.com/2009/06/asyncapi/dataload">
<operation>insert</operation>
<object>Objectname</object>
<contentType>CSV</contentType>
</jobInfo>

and how to create the csv file for it?Any ideas? I would like to know the steps for it?

Thanks in advance