If a document is accessible by the public, then it is also accessible by Search crawlers. This means it will appear in search results. Any time a document is linked on a page, the likelihood of a document appearing higher in a list of search results increases.
You can Hide a document from the public, which means the document will be excluded from Search Results and will not show on the front-end Document Center page. Users with a direct link will still be able to access the document.