BASALT · JOURNAL
Redacting hundreds of documents without doing it hundreds of times
Batch processing is the obvious answer to a large production and it is only partly correct. Some redaction work batches safely and some of it must not, and the distinction is worth being precise about because the failure mode is disclosure.
What batches safely
Operations that do not depend on what is on the page. Stripping metadata, removing attachments, flattening layers, applying Bates numbers, adding a watermark, compressing, and running OCR are all mechanical and identical in intent across every file in a set.
These should absolutely be batched, and running them one at a time on 500 files is simply wasted hours.
What does not batch
Deciding what to remove. Marks are positional, and the same rectangle on page 3 of document A covers a client name while on page 3 of document B it covers a paragraph of unrelated text. Applying one set of marks across a set is not redaction, it is drawing rectangles in arbitrary places, and the consequence is both over redaction and, worse, material left exposed.
Search based marking sits in between. Finding every occurrence of a name across a set is genuinely useful and genuinely batchable, but the results still need review, because a surname that should be removed in one context appears legitimately in another.
The shape that works
Batch the mechanical passes across the whole set. Mark each document individually, or mark by search and review the hits. Then batch the export.
That way the expensive human judgement is spent only where judgement is required, and everything else runs unattended.
Timing a batch
Cost follows marked pages rather than documents. Measured, a scanned page with a mark on it costs about a second to redact, and a text page about a tenth of that. A 500 document set with an average of three marked scanned pages each is around twenty five minutes of machine time.
Run it before the deadline. The work is deterministic, so the estimate holds, and nothing about a large batch benefits from being started late.
What to demand from a batch tool
A plan shown before the run starts, so you can see what will happen to which file. Per file results afterwards, including failures, rather than a single completion message. And a run that stops on a failure rather than skipping quietly, because a document that silently failed to redact is the one that gets produced.
Frequently asked questions
Can you batch redact multiple PDFs?
The mechanical parts yes, the decisions no. Stripping metadata, flattening, Bates numbering, watermarking, compression and OCR batch safely across a set. Deciding what to remove does not, because marks are positional and the same rectangle covers different content in different documents.
Why is applying the same redaction marks to many documents dangerous?
Because a mark is a position on a page, not a concept. The same rectangle that covers a client name in one document covers unrelated text in another, and elsewhere in the set the material that should have been removed is left exposed.
Can you redact by searching across many documents?
Yes, and it is the most useful batch approach, but the hits need review before they are applied. A search for a surname will match contexts that should not be redacted, so treating search results as final produces both over redaction and errors.
How long does a batch redaction take?
Cost follows marked pages rather than document count. Around a second per marked scanned page and a tenth of that per marked text page, so 500 documents with three marked scanned pages each is roughly twenty five minutes.
Doing it in Basalt
Basalt is a native macOS PDF toolkit with eighteen tools in one window. It opens large documents without loading them into memory, renders pages on demand, and copies files into its engine in fixed-size chunks, so peak memory follows the chunk size rather than the file size. Redaction destroys content rather than covering it, and an independent verifier re-opens every written file to prove the material is gone before the file is saved. A one time $29 licence covers up to three Macs, it is free for the first 24 hours, and the engine holds no network entitlement at all, which macOS enforces at the code-signature level. Download it at basaltformac.com.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.