Use the universal search to link to any content
You can use the universal search to link to any content (this can be diagrams, pages or attachments) within Confluence.
In the Link Edit menu choose Search and begin your search query by typing in the search field. Then using the pull-down menu on the right of the search field, you also have the option to specify a Confluence space to search within if you don’t want to search all spaces. Please note that the search follows Confluence permissions. This means that you can only link to content that you have been given permission to view.