If you're working for a company, you could consider buying a packaged solution. One I've seen advertised is Nuix. Also, Oracle has an end-to-end solution for GDPR (the new EU privacy law), which includes the kind of functionality you describe. See http://www.oracle.com/technetwork/database/security/wp-security-dbsec-gdpr-3073228.pdf.
If you have the Oracle RDBMS, there is a package called CTXSYS (now called Oracle Text) which has amazing search capabilities across documents, including PDFs, the entire Office suite, and many more. CTXSYS is included in the regular license. If you're a home user, you can download Oracle server (the Express version is fine for this function).
If you're using regexes as suggested above, one simple approach would be to search for words that are capitalized in mid-sentence, but that only helps with documents (not so much with XLS, for example). You could also build a dictionary of common names (first/last names, streets, towns). The credit cards and SSNs should be readily regex-able.