How to scan network drives for PII (SSN)

I am trying to create a powershell script to scan our network drives for PII, specifically SSN number patterns. I am having trouble figuring out how to scan pptx, pdf and xlsx file content using powershell. Do you have an idea how I might accomplish this?

Why not just use Windows FSRM / FCI to do this?

Just serach for ‘Windows fsrm fci find pii’

Using File Server Resource Manager (FSRM) to Locate and Classify Sensitive Data such as Credit Card Numbers Stored Inside of Documents

Corporate policy states that sales employees should not be storing customer credit card information especially credit card numbers on the file servers. As the administrator of the file sever you have been tasked with locating any files that have what look like suspected credit card numbers based on known numerical stings. You want to automate the process and classify the card based off of vender.

Storage at Microsoft - Microsoft Tech Community