Manatee

How to compress a PDF on a Mac

· 7 min read

The quickest way to compress a PDF on a Mac is Preview: open the file, choose File > Export, and pick “Reduce File Size” from the Quartz Filter menu. That works in a few seconds, but it is blunt and often leaves images looking rough. If you care about how the pages look, or you need to hit a specific size, build a gentler custom filter in ColorSync Utility or use a tool that lets you name the target size and finds the quality to match.

Why a PDF is big in the first place

A PDF that is mostly text is rarely large. A ten-page contract with no pictures is usually well under 1 MB. When a PDF balloons to 20, 50 or 200 MB, one of three things is going on:

  • Images at print resolution. A photo placed in a Pages or Word document gets embedded at its original size. Four phone photos can add 30 MB on their own.
  • Scanned pages. A scanner saves every page as a full-color image, often at 300 or 600 dpi. There is no text underneath, just pixels. This is the most common reason a “simple” document is enormous, and it has its own guide: how to compress a scanned PDF on a Mac.
  • Embedded fonts and leftovers. Design apps sometimes embed whole font families, layers, or the original artwork. Less common, but they add up.

Knowing which one you have tells you what to do. Image-heavy files respond well to downsampling. Scans need downsampling plus a change to grayscale. Files that are big for structural reasons usually need re-exporting from the app that made them.

The fast way: Preview’s Reduce File Size filter

Preview’s filter is the right first attempt when you just need the file to go through and nobody is going to frame the pages.

  1. Open the PDF in Preview.
  2. Choose File > Export (not Export as PDF, which skips the filter options).
  3. Leave Format set to PDF.
  4. Open the Quartz Filter pop-up menu and choose Reduce File Size.
  5. Give the file a new name so you keep the original, then click Save.

Preview will downsample every image and compress it with JPEG at a low quality setting. On a photo-heavy document the result is often a tenth of the original size. The cost is obvious when you zoom in: pictures go soft, and fine diagrams can become hard to read. Text is untouched, because text in a real PDF is stored as vectors, not pixels.

If the output is good enough, you are done. If it looks worse than you can accept, move on to the next method.

A better filter with ColorSync Utility

The “Reduce File Size” filter is just a preset, and macOS lets you make your own with more sensible numbers. This takes five minutes once and then appears in Preview’s menu forever.

  1. Open ColorSync Utility (it lives in Applications > Utilities, or search for it with Spotlight).
  2. Click the Filters tab.
  3. Find Reduce File Size in the list. Click the arrow at the right end of its row and choose Duplicate Filter.
  4. Rename the copy to something like “Reduce File Size (gentle)”.
  5. Expand the copy and open Image Sampling. Set Resolution to 150 pixels per inch for screen reading, or 200 if the document might be printed. Leave Scale at 100 percent.
  6. Open Image Compression, set Mode to JPEG, and move the Quality slider to about the middle.
  7. Close ColorSync Utility. The filter is saved to your user account automatically.

Now go back to Preview, choose File > Export, and your new filter is listed in the Quartz Filter menu. The result is typically two to four times smaller than the original, with photos that still look like photos. If you need it smaller, lower the resolution to 120 and the quality a notch further, and export again from the original (not from the already-compressed copy, since each pass throws away more).

Re-export from the app that made it

If you still have the source document, exporting again with lower image settings usually beats compressing the finished PDF, because the app can start from the full-quality originals.

  • Pages: File > Export To > PDF, then set Image Quality to Good rather than Best.
  • Word for Mac: File > Save As, choose PDF, and pick “Best for electronic distribution and accessibility” rather than “Best for printing”.
  • Keynote: File > Export To > PDF, set Image Quality to Good and untick “Include presenter notes” if you don’t need them.
  • Photoshop, Affinity, and other design apps: look for a “PDF (smallest file)” or “web” preset, and make sure layers and editing capability are not preserved.

Re-exporting also strips anything the original export left behind, such as a second copy of every image for print. It is the cleanest fix when it is available.

Compress to an exact size with Manatee

All of the methods above share the same weakness: you pick a quality setting, export, check the size, and try again if it missed. When a portal says “10 MB maximum” or a recruiter says “keep it under 2 MB”, the number is the goal, and guessing at dpi values is a slow way to reach it.

Manatee approaches it from the other direction. Open the app, switch to Shrink, drop the PDF in, and type the size you need in MB. Manatee tries progressively stronger image settings until the file fits, then writes a new copy next to the original. The original is never touched, and nothing leaves your Mac; the whole job runs locally. Every feature is free for the first 24 hours, so a single PDF emergency costs nothing.

Two limits worth knowing. Manatee shrinks by recompressing and downsampling images, so a PDF that is already pure text with no pictures will not get much smaller, because there is nothing left to squeeze. And it does not edit the document: it cannot delete pages, remove fonts, or change text. If you need to drop pages, do that in Preview first (select the thumbnails in the sidebar and press Delete), then shrink what remains.

What compression cannot fix

A few cases where no filter will get you there:

  • A large page count with a large image on every page. At some point the only fix is splitting the file. In Preview, drag page thumbnails out to the desktop to create separate PDFs, or use File > Print > Pages range, then save as PDF from the print dialog.
  • Password-protected PDFs. Filters cannot rewrite an encrypted file. Open it with the password, export an unlocked copy, then compress that.
  • PDFs that are big because of attachments. Some PDFs carry embedded files (spreadsheets, other PDFs). Preview’s sidebar doesn’t show these; if a text-only PDF is mysteriously 40 MB, that is a likely cause, and you need the source document.

If the goal is privacy rather than size, compression does nothing to the author name, creation app or edit dates stored in the file. That is a separate job: how to remove metadata from a PDF on a Mac.

Questions

Does compressing a PDF make the text blurry?

Not in a normal PDF, where text is stored as vector outlines and is untouched by image filters. It will look blurry if the PDF is a scan, because then the “text” is actually a picture. For scans, downsample carefully and keep the resolution at 150 dpi or higher.

Why did Preview’s Reduce File Size make my PDF bigger?

It happens with PDFs that contain hundreds of minuscule images or already heavily compressed ones. The filter re-encodes each image and adds its own overhead, which can exceed the savings. Use a custom ColorSync filter with a higher quality setting, or re-export from the source app.

Can I compress several PDFs at once?

Preview works one file at a time. Manatee’s window has a drop zone and a job list, so you can drop several PDFs and watch them work through in turn. If you have a stack of upload-portal documents to get under a limit, that is the practical route: see how to get a PDF under 10 MB for an upload portal.