BASALT · JOURNAL
Getting a PDF under 10 MB
A 10 MB limit is common on corporate mail servers and court e-filing systems, and it is tight for anything scanned. This is the order that works.
Establish what you are dealing with
File size divided by page count. Over 100 KB per page means scanned images and everything below applies. Under that, the document is mostly text and 10 MB should be easy, so something specific is bloating it: usually an embedded image repeated on every page, or a full embedded font set.
For scanned documents
Greyscale first. Colour scans of black and white documents are paying three times over. This alone frequently gets a file under the limit and loses nothing real.
Then resolution. 300 DPI is the working floor for documents that may be read closely or OCRed. If the scan is at 600, halving it removes about three quarters of the pixels.
Then JPEG quality, carefully. This is where legibility goes. Text edges develop halos before photographs look damaged, and on a document that may be read in court that is a real cost.
Measure, do not predict
Output size depends on image content rather than dimensions, so estimates are unreliable. Compress, check the actual result, and adjust. A tool that measures the real output before replacing the file can also guarantee it never hands back something larger, which is a genuine failure mode when re-encoding already compressed images.
If it still will not fit
Split it. A hard limit with a document that genuinely needs its resolution is a case for two files rather than an unreadable one. Splitting is lossless.
For court filings, check the rules before splitting: some systems specify how multi-part documents must be named and indexed, and getting that wrong is worse than a size problem.
What not to do for a filing
Do not compress the copy you keep. Compress a copy for transmission and retain the original as received. If anyone later disputes what a page said, the answer should come from the unmodified file.
Frequently asked questions
How do I get a PDF under 10 MB?
For scanned documents: convert to greyscale if the original is monochrome, reduce resolution to no less than 300 DPI, and only then reduce JPEG quality. Check the actual output size at each step rather than predicting it.
Why is my PDF so large when it is only a few pages?
Divide size by page count. Over roughly 100 KB per page means scanned images. Under that, look for a large image repeated on every page or a fully embedded font set.
Is it better to compress or split a PDF?
Split when the constraint is a transfer or filing limit, because splitting is lossless and compression is not. Compress only when the recipient genuinely needs a single file.
Should I compress a PDF I am filing with a court?
Compress a copy for filing and keep the original unmodified. Also check the court's rules on multi-part documents before splitting, since naming and indexing requirements vary.
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.