Guest users can't preview a document in the global search page even if the document and its parent folder have View and Access permissions enabled, but are able to preview the document using documents and media widget inside a page.
I m using liferay-ce-portal-7.3.5-ga6 with Ubuntu 18.04.5 LTS.

How to reproduce:

1- Create a Global search page
2- Create a folder in documents and media with permissions for guests (View and Access)
3- Upload a simple document (e.g pdf) and make sure it has View and Access permissions for guests.
4- Search for the document on the global search page.
5- Click in the document while logged in
    - Realise you can preview document
6- Logout 
7- Search and click in the document
    - Realize you only can see an empty page without any errors in the server or in the browser console.