Document Share Public
This app allows users to share the documents attached along with Odoo records via a public URL. The screen shows a sale order record with two attachments.

At the bottom of the record, in the chatter area, will appear the new link “Attachment Link”.

The Action will open a pop up where users can see the list of attachments related to the record(sale order).

Clicking on the link against selected document will open a new window with public URL of the attachment(document).

The URL, from any browser, will open the document directly.

Please refer link to the module in Odoo Apps.
https://apps.odoo.com/apps/modules/11.0/bt_document_share_public/