Hi Nikhil,
Well seeing th file format and your exposure to IDoc I will not recommend the method unless the buyer can send you the file in an IDOC / XML format.
You can use the BAPI method
You can put the files in you app server and read the files from there using a program that is a scheduled job
Read the contents and convert to BAPI structure and update.
Create a Z log table for the entries.
For details on which BAPI to use and how to use please refer to below link it contains a document mentioning the same.
Regards