BASALT · JOURNAL
Splitting a PDF into equal parts
Splitting is lossless: pages are copied without re-encoding, so each output is byte for byte what it was in the original.
Every N pages
qpdf input.pdf --split-pages=50 part.pdfThat writes fifty page chunks named part-01.pdf and so on. Useful when the constraint is arbitrary, such as a reviewer who wants manageable pieces.
Single pages
qpdf input.pdf --split-pages=1 page.pdfCommon when preparing exhibits or when a system ingests one page at a time.
By file size
Page count is the wrong unit for scanned documents, where a blank page is a few kilobytes and a dense colour page is several megabytes. A fifty page split can produce chunks that differ tenfold.
When the constraint is an upload or attachment limit, split by measured output size instead, accumulating pages until the next one would exceed the limit. Measured rather than estimated, because shared resources such as fonts and images make predictions unreliable.
At document boundaries
A production is usually many documents concatenated, and splitting at arbitrary page counts cuts them in half.
If the file has bookmarks they often mark those boundaries. If it has Bates numbers the ranges do. Splitting blindly is the last resort rather than the default.
After splitting
Check that the parts account for every page of the original. An off by one at a boundary is easy to make and awkward to discover later.
Each part also inherits the original's metadata, including anything naming the source document and its author. If the parts are going to another party, that is worth checking before sending rather than after.
Frequently asked questions
How do I split a PDF every N pages?
qpdf input.pdf --split-pages=50 part.pdf writes fifty page chunks. Use --split-pages=1 for single pages.
Does splitting a PDF lose quality?
No. Pages are copied without decoding or re-encoding, so each output contains exactly the original content. Quality loss comes from compression or conversion, not splitting.
Should I split by page count or file size?
By size when the constraint is an upload or attachment limit, because scanned pages vary enormously in size and a fixed page count produces wildly uneven chunks.
What should I check after splitting a PDF?
That the parts account for every page of the original, and that their metadata does not carry information about the source document you would rather not send.
Doing it in Basalt
Basalt is a native macOS PDF toolkit: eighteen tools in one window covering merge, split, page organisation, compression, OCR, passwords, Bates numbering, forms, signing, watermarks and comparison. Every file is processed on your Mac, and the engine that opens documents holds no network entitlement at all, which macOS enforces at the code-signature level. Redaction destroys content rather than covering it, and an independent verifier proves the material is gone before a file is written. A one time $29 licence covers up to three Macs, free for the first 24 hours. Get it at basaltformac.com, or brew install --cask chipmunk1101/tap/basalt.
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.