Dedicated asset link

I have a client that wants to have a dedicated url for an asset. they have regularly sent out emails for years with a link to a PDF. that link has remained the same throughout. we now post the document on their site, however, their users have saved the dedicated url

in contentful, i’m running into the problem where I update the upload attachment and the url changes from


any ideas as to how I can recreate the dedicated link as described above?