By default, Windows will use the index when searching to give you faster search results. The search index only includes your selected locations. These locations can be filtered for what file types (extensions), file properties, and file contents you want indexed.
The index uses the Windows Search service and runs as the Searchindexer.exe process in the background. The index will automatically rebuild and update for changes made to the included locations since the last index rebuild to increase search result accuracy. By default, the indexing speed is reduced due to user activity. If the computer is running idle, then the indexing speed will go back to full speed to finish indexing faster.
Windows Search 4.0 and higher fully supports indexing encrypted files on local file systems by EFS, enabling users to index and search the properties and contents of encrypted files. Users can manually configure Windows Search to include encrypted files, or administrators can configure this with Group Policy. Windows Search ensures that only users with the correct permissions can search the content of encrypted files by honoring ACLs and by restricting access to users with decryption permissions for the files. Additionally, Windows Search restricts access to encrypted files to local searches only; Windows Search does not return encrypted files in search results when the query is initiated remotely.
This tutorial will show you how to turn on or off to index encrypted files for all users in Windows 10.