How do I run a PowerShell script on a file from the context menu?

Question

I have written a PS script, which replaces a specific string at the beginning of the file, adds another piece of string to the end of the file, and finally it puts out an XML.

My code might be ugly (I am not a programmer/engineer or anything, just trying to make life easier for some family members who are running a small business), but it works:

$content = Get-Content -Path 'C:\Users\blabla\Desktop\4440341930.txt'
$newContent = $content -replace 'text to be replaced','this is going to replace stuff'
$newContent | Set-Content -Path 'C:\Users\blabla\Desktop\4440341930.txt'
Add-Content C:\Users\blabla\Desktop\4440341930.txt '</Items>'
$x = [xml](Get-Content "C:\Users\blabla\Desktop\4440341930.txt")
$x.Save("C:\Users\blabla\Desktop\4440341930.xml")

I would like them to be able to run this script from the context menu, by right clicking on a txt file. I did a little research and I kind of get what I have to add to Registry, however, I'm not sure how to make it work. Since the path of each file that they are going to right click on is going to be different, the path that I'm specifying in $content is not going to work.

What do I have to modify in my code to be able to add it to the Registry?