Win8.1 Searching for Files in File Explorer

To search for files in File Explorer, open File Explorer and use the search box in the top right corner.
Open this “ this computer by: swiping from the right edge of the screen to the middle, click "Search" (If you use the mouse, point to the upper right corner of the screen, then move the mouse pointer down , click “search”), enter this computer in the search box, and then click or click “this computer”.
The search function will look in all folders and subfolders where you view the location. When you click or click within the search box, the “Search Tools” tab will be displayed. When you enter a search term, the results will begin to appear, with the search term highlighted.

Search Results in File Explorer
The following operations can also be done using the search box and the "Search Tool" tab:
To search for a specific file extension (eg .txt ) For all files, you can enter a search term similar to *.txt.
You can search based on the last modified date of the file or the file type (eg “image”). Once you've entered your search term, click or click the "Search Tools" tab, use the "Optimize" option in the group, and enter your search term in the search box. For example, if you only want to search for a file name instead of a file content, click or click “other properties", select “name”, and enter a search term.
If you can't find what you're looking for in a particular library or folder, you can expand your search to include other locations. Once the search results appear, click or click the “Search Tools” tab and select an option under “Search again in the following locations. (Some options may not work in Windows RT.)
If the search results do not contain any file content matches, then the location you are searching for is not in the search index. To include file content in a single search, click or click the “Search Tools” tab, then tap or click “Advanced Options” and select “File Content”. To add this location to the index so that the file content is always included in the search, click or click the "Search Tools" tab, then tap or click “Advanced Options”, then select “Change Index Location & rdquo;.