Reduce the File Size of PDF Documents with Preview in Mac OS X

Dec 12, 2013 - 8 Comments

PDF The PDF file format is ubiquitous for good reason, mostly because it allows for perfect preservation of a documents formatting, text, and other elements, but also because it allows for encrypted password protection of documents. But let’s face it, sometimes PDF files can be bloated, and something that should be 200k or less can be 1.2MB for no obvious reason, particularly if they have been generated at the OS level from something like printing to a PDF, another file that has been converted to a PDF, or created with an app that just doesn’t offer any compression at all.

For PDF files that have not been optimized yet, the Preview app in OS X can often reduce the file size considerably by passing it through an export filter. While it works great for text heavy files, it’s not a perfect solution for every document out there, so you’ll want to run through the process with the document in question and compare it to the original to see if it helps. Let’s get to it:

  1. Open the PDF file that you want to reduce the size for in Preview app (typically the default PDF viewer in OS X)
  2. Pull down the “File” menu and choose “Export”
  3. Export a PDF to compress the file size in Preview app for Mac OS X

  4. Select the submenu next to “Quartz Filter” and choose “Reduce File Size”
  5. Save the new reduced version of the PDF as usual by hitting “Save”
  6. Reduce File Size filter in Preview app for PDF files

(Note: you can also access Quartz Filters through “Save As” with new versions of Preview for OS X, but the File > Export trick works for prior versions of the app as well)

Just how much space you will save by using this file reduction filter varies greatly, depending on the content of the PDF, the original app that created and saved the PDF and if any filtering was applied to begin with, amongst a variety of other factors. For originating documents that are entirely text, like a resume or a Word document that’s been converted to a PDF without any sort of optimization, it can make a huge difference, and you may see a file sized from 1MB shrinking down to under 100k.

Keep in mind that Quartz Filters are basically image processing filters, but unlike apps made for lossless image compression, the PDF file will be processed in such a way which may result in lossy compression and artifacts appearing on embedded imagery. That’s not always desirable, which makes this trick best for PDF files that are heavy on text, simple graphs, charts, spreadsheets, or basic vector drawings, and not complete images or photos where high image quality is desired. Again, this is a benefit to using the “Export” command, since you can compare the two documents easily when it’s finished, which is recommended.

Counterintuitively and in some less common situations, beginning with an already optimized and compressed PDF file may result in a larger file being generated using this reduction filter. This really depends on the application that created the PDF to begin with and if the file was compressed at all, but for situations where a PDF is generated through something like Adobe Acrobat Pro you may find it to be the case.

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Posted by: Paul Horowitz in Mac OS X, Tips & Tricks

8 Comments

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  1. RB says:

    Yup, works well on text PDF, not well on image heavy PDF.

  2. Ben says:

    Preview always uses the same filter. But there are some apps on the Mac App Store that allow you to choose from different filters such as PDF Squeezer.

  3. Darryn says:

    Hey how did you get the ‘save-as’ command in Preview? I’m on lion 10.7.5 and it was dropped since the last osx upgrade….so annoying :(

  4. Steve says:

    Works absolutely great thank you for your help.

  5. Michelle says:

    This reduced a file from 4MB down to 38kb—way too small. I tried to find a way to change the default setting but couldn’t do it. I wonder what happened to the “save as” key?? (I just upgraded to Mavericks from Snow Leopard)

    • Becky says:

      Instead of export to “Reduced Size File”, choose Gray Scale instead. Mine reduced from 8MB to 350KB instead of 51KB wehn I chose Reduced Size File.

  6. alissa says:

    Doing this just doubled my PDF file size (from 3. .3 MB to 6.7)… ???

  7. JohnB says:

    The issue I had was that a 20mb pdf (derived from a 40mb png file from a scanner) was reduced to a 20kb file that was very grainy, albeit perfect for viewing as an icon, not so good when using it as a scanned building layout.
    My solution was to scan the 8″x11″ document in a lower resolution (300x300dpi) then converting it to pdf. The size was a reasonable 5.5mb afterwards.

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