Reference layout item
Insert a Reference from Add. Pick a Doc from the picker — the search field uses Search documents…. Display can be Wide, Small, or Card. Untitled targets show as Untitled.
Copy a link
Context menus can copy a Doc link. Opening that link in the app takes you to the Doc if you have access — as owner or as an editor on a share (including inherited descendants).
Not a public URL
A Doc link is not a public share. People without a grant or ownership cannot open it. To collaborate, use Sharing.