I am seeing a tab in soap client as attachment. What is the use of that?

Hi,

The tab named "attachment" in the SOAP Client is used to configure SOAP Attachments. They are part of a specification for how to send MIME multiple messages in combination with a SOAP Message.

Tool's documentation
https://docs.parasoft.com/display/SOAVIRT9107/SOAP+Client#SOAPClient-AttachmentOptionsAttachmentOptions

General summation of SOAP Attachments
https://en.wikipedia.org/wiki/SOAP_with_Attachments

Also see my answer in your original thread (this one is a duplicate):
Attachment in Parasoft