https://regex101.com/ handy website to check your regex results
Regular Expression Language – Quick Reference
Simple comparison to find a part of a line that matches “.*.enc” where the * is 3 characters or more and each character is a-z or A-Z
the \ is used to escape the .
($LineToCheck -match "\.[a-zA-Z]{3,}\.enc")
e.g.
.docx.enc
.doc.enc