Google Drive API "Insufficient permissions for this file" error with Service Account

Question

I am trying to delete permissions on a specific file in Google Drive using Google Drive API and Google Apps Script with a service account.

My mission is to delete permission of a file which is shared with the option "public on the web".

Things I have done so far:

1. Created a service account with domain-wide delegation.

2. I have included following scopes in admin.google.com

   https://www.google.com/m8/feeds
   https://www.googleapis.com/auth/admin.reports.audit.readonly
   https://www.googleapis.com/auth/drive
   https://www.googleapis.com/auth/script.external_request

error log:

"error": {
  "errors": [
   {
    "domain": "global",
    "reason": "forbidden",
    "message": "Insufficient permissions for this file",
    "locationType": "other",
    "location": "file.permissions"
   }
  ],
  "code": 403,
  "message": "Insufficient permissions for this file"
 }
}