It the only, but maybe the easiest.

Having a data review process with automated integrity, confidentiality, and quality checks is not terribly difficult.

But having a prototocol to export the pdf to csv is also dead easy for confirming only the data relevant is included. ASCII is just as “easy” as scan, but it requires training clerks to be data-oriented rather than document.

But as the public is typically entitled to that "other stuff" information as well, you're just obstructing.

PDFs can and do send non visible data that wasn’t intended to be transmitted.

It's more of a way to prevent transmitting any easily accessible data at all. Using a human-auditable but still machine-readable format like CSV is what should be done.

There are other ways to ensure this. Even with your own logic, it would make sense then to send both the Excel sheets and scanned PDFs of the Excel sheets, isn't it? It would be super comical though