There is a way to do this without code. It does, however, leave some unfortunate visual artifacts. I am hoping that this will be seen as a bug and fixed.

Here is how to try it yourself:

Select a Button while editing, and then on the right side scroll down to "Inline Text" and then select "Insert Media", you can upload a document that will be downloaded upon click.

You insert your pdf in the EDM of odoo, then you paste the sharing link of this document from your EDM into your button. So people will be sent to the pdf

Hi Tentiana,

Could you please add a new button and link it to this type of URL?

t-attf-href="/web/content/#{attachment.id}?download=true&access_token=#{attachment.access_token}"

You can search for Odoo addons using this URL.