Since PowerShell 3.0, there is a built-in cmdlet designed specifically for this task. It is the safest and easiest method.
Few things are as frustrating as trying to delete, move, or edit a file, only to be met with the error: powershell unlock file
& "C:\path\to\handle64.exe" -accepteula "C:\path\to\your\file.pdf" Since PowerShell 3