How to Compress a PDF to a Specific Size on Mac

A PDF is usually large because of the images inside it: scanned pages, photos and screenshots. Text, fonts and vector drawings take up very little space in comparison.

A scanner that saves every page at high resolution, or a report built from full-size phone photos, can easily reach tens of megabytes. Shrinking it means storing those images at a lower resolution or with stronger JPEG compression, ideally only as much as your limit requires.

Preview can shrink a PDF with its Reduce File Size filter: choose File > Export, pick Reduce File Size from the Quartz Filter menu and save.

The problem is that it's one fixed recipe. You can't tell it “under 2 MB”, so a large scan may still be too big, while a small file can come out blurry, with washed-out photos. Custom filters built in ColorSync Utility give more control, but you still set resolution and quality by trial and error, one file at a time.

In File Acture, set Compress by to Target size, type the limit, and the app searches for the highest image quality that still fits. The search tries image resolutions from 300 down to 72 DPI and a range of JPEG qualities, measures the real file size and corrects itself, so the result lands at or just below your target.

In a test on an Apple M4 running macOS 26, a 54 MB, 36-page PDF came out at 4.84 MB for a 5 MB target in 1.38 seconds, and at 1.94 MB for a 2 MB target in 1.02 seconds, with its images at 170 DPI. Text and vector graphics were not touched.

The Presets menu offers 1, 2, 5, 10 and 25 MB, and you can type any value in KB or MB. File Acture uses decimal units like Finder, so a file under 2 MB also passes a site that counts a megabyte as 1,024 KB. If the PDF already fits, it's only tidied up, not re-encoded. If it can't get as small as you asked, File Acture tells you the smallest size it can reach instead of saving a ruined file.

Often, yes: a few scanned pages or a short photo report usually fit in 1 MB at a readable quality. A long, photo-heavy document may only get there at low resolution, and File Acture says so when it can't.

• Try grayscale. Convert images to grayscale helps with colored scans of documents that don't need color.
• Split it. If the portal accepts several files, split the PDF into parts and give each part its own target.
• Drop the metadata. Remove document metadata clears the title, author and similar fields. It saves little space, but it keeps personal details out of the file.

Compression works on images, so a PDF made mostly of text, fonts or vector art shrinks very little.

• Scans that were already saved at low quality have little left to give.
• Black-and-white scans stored as JBIG2 or CCITT, and CMYK, JPEG 2000, indexed or 16-bit images, are left as they are.
• A PDF that needs a password to open has to be unlocked first with Unlock PDF; protect the smaller copy again afterwards.

Online compressors upload your PDF, which is a real risk for contracts, payslips and ID scans. File Acture compresses on your Mac and never uploads the file, and Pro works without an internet connection, going online only now and then to renew its license.

The free version includes 3 runs on each Mac, with up to 5 PDFs per run, and Pro removes the limits; see pricing. For single photos, Compress Images does the same job with a target in KB.