Creating keyword relevant file names not only improves SEO but also helps to improve your pages in topic relevant manner. You need to create folder names with relevant keywords as well as file names. You can see well optimized file name sites ranked higher than series of numbers or meaningless alphabetical letters file name pages. By creating a keyword with descriptive document name, the visitor can easily recognize the URL and enter on your site.
Use keyword in your folder and file names and it must be shorter.
The shorter the name of the web document, the easier the visitor can remember it.