Where I work, the physical document is first scanned into an electronic form (multipage formats like TIFF or PDF, usually). The electronic document is then impo

Where I work, the physical document is first scanned into an electronic form (multipage formats like TIFF or PDF, usually). The electronic document is then imported into a proprietary redaction program (there's quite a few on the market, most copier/scanner vendors have an offering). It then assists with the initial redaction by performing OCR on the content, allowing you to quickly search for sensitive information. The software provides built-in tools for blacking out sensitive sections of the document - some even provide configurable overlays/stamps on the blackouts for why that section was redacted. Then one or more humans manually go over the documents to make sure that nothing was missed. When they are happy with the results, the document is finalized into a TIFF or PDF document with the pages flattened into single image objects (so you can't just delete the black boxes - they are now part of the embedded image). The original documents do not need to be harmed in any way, they just need to be able to be scanned to start the process. Conversion to an image format helps to ensure that if the source was an electronic document that sensitive original source metadata or proprietary document format binary blobs don't inadvertently leak redacted information. If a physical copy is required, you just print it.