As default SharePoint Search results displays the “Title” of a document instead of the “Filename“.
This behavior is sometimes really annoying and doesn’t work for the end users.
The easiest way to change this behavior is to change the “Search Schema”
Navigate to your Central Administration or O365 Search Administration | “Manage Search Schema”
Search for the managed property “Title”
Add the crawled property ” ows_LinkFilename” as “a Mapping” to this property and move it to the top | OK | and re-crawl your content
Search Results should now display the Filename before the Title