I have a link on my server that lets users download the .jad file I have got. But when I open this link in Google Chrome, it opens it as a text file rather than downloading the .jad file.
Update mime type configuration for your server and set mime type of *.jad file extension to 'application/x-download'. This should make browser client downloading the file instead of rendering plain text of the file.
For example, if you are using apache http server you can update mime.types file by adding following line
application/x-download jad