Content-disposition header is important because it tells the browser not to load this content but download it instead it can also define the file name of the file getting downloaded so it's an opportunity to raise a file download dialog box.
The Content-Disposition response-header field allows origin server to provide a suggested filename if the user want to save it to specific file they want to save it to.
Some code examples for Content-Disposition:
content-disposition = "Content-Disposition" ":"
disposition-type *( ";" disposition-parm )
The main line of code for this:
Content-Disposition: attachment; filename="File123.ext"
See following links for details: