BASALT · JOURNAL
How long it takes to redact a 1,000 page PDF
Redaction speed depends almost entirely on whether the page is text or an image, and the difference is about two orders of magnitude per page. Anyone planning a large production should know which they have before estimating the time.
Text pages are fast
Removing text means finding the glyphs inside a mark, dropping them from the content stream, and re-emitting the survivors so the remaining line still renders correctly. That is string and array work.
Measured: 500 marks spread across 300 text pages took 36 seconds, including the verification pass that re-opens the written file and proves the terms are gone. That is roughly a tenth of a second per marked page.
Scanned pages are slow
A scanned page has no text to remove. The words are pixels inside a JPEG, so redacting means decoding the image, destroying the pixels under the mark, and re-encoding the result. Decode and encode are the expensive parts and there is no way around them, because leaving the original image in place is exactly the failure this is meant to prevent.
Measured: 300 marks across 200 scanned pages took 191 seconds. That is 0.96 seconds per marked page, and it scales roughly linearly, so a 1,000 page scanned production with a mark on every page is in the region of sixteen minutes.
The machine was an Apple M1 Pro with 16 GB, running under Rosetta, so a native build should do better rather than worse.
Planning around it
Sixteen minutes is not a problem if you know about it in advance and a serious one if you discover it at 4pm on a filing deadline. Three practical consequences.
Run large scanned productions before you need them, not while someone waits. The work is deterministic, so the estimate holds.
Mark pages rather than whole documents where you can. Cost follows marked pages, not total pages: a 1,000 page document with marks on 40 pages costs about forty seconds, not sixteen minutes.
Check that whatever you use can be cancelled mid-run and tells you where it has got to. A long job with no progress and no cancel is the actual usability failure, more than the duration.
Why not just cover the text and move on
Because that is not redaction, and on a scanned page it is especially misleading. A black rectangle drawn over a photograph of a document leaves the photograph intact underneath, and removing the rectangle is a single operation in any PDF editor. The pixels have to be destroyed, and destroying them means re-encoding the image, which is where the time goes.
Frequently asked questions
How long does it take to redact a large PDF?
For text pages, roughly a tenth of a second per marked page: 500 marks across 300 pages measured at 36 seconds including verification. For scanned pages it is about a second per marked page, because each image has to be decoded, altered and re-encoded, so 300 marks across 200 scanned pages measured at 191 seconds.
Why is redacting a scanned PDF slower than a text PDF?
A scanned page holds no text to remove. The words are pixels inside a compressed image, so the image has to be decoded, the pixels under the mark destroyed, and the image re-encoded. Decoding and encoding dominate the time, and skipping them would leave the original picture in the file.
Does redaction time depend on total pages or marked pages?
Marked pages. An unmarked page is copied through without being decoded or rewritten, so a long document with a few marks costs about the same as a short document with the same few marks.
Can you redact a 1,000 page production in one run?
Yes. Expect roughly sixteen minutes if every page carries a mark and the pages are scans, and well under a minute if the pages are text. Run it before the deadline rather than during it.
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.