To make a PDF smaller in Preview on a Mac, export a separate copy with File > Export > Quartz Filter > Reduce File Size, then compare the result with the original at normal reading size and at a closer zoom. Compression can lower image quality, and the amount of size reduction varies. Keep the original until you have checked text, fine details, and any pages that matter most. Apple’s Preview guide

First, decide what “readable” means for this PDF

A text-heavy handout, a scan of small print, and a photo-rich report have different weak points. With selectable text, the letters may remain crisp while photographs or embedded scans lose detail. With a scanned document, much of the page may be an image, so compression can soften both letters and fine lines. These are practical distinctions to inspect in the output; Apple cautions that compression can lower quality and that file size and image quality vary with the options used. Apple’s Preview guide

Before exporting, open the original PDF in Preview and check a representative page: one with the smallest text, one with a chart, signature, or fine linework, and one with a photograph if the document contains images. Note any tiny labels or details that must stay clear. This gives you a comparison target instead of relying on the file-size number alone.

Make a smaller copy with Preview’s built-in filter

  1. In Preview, open the PDF you want to reduce.
  2. Choose File > Export.
  3. In the Quartz Filter menu, choose Reduce File Size.
  4. Save under a new filename, such as report-smaller.pdf, so the source remains available.
  5. If macOS asks whether to replace the existing file, choose the option that keeps your original and save the new copy under a different name.

Apple documents this export path and specifically describes saving with a different filename when you do not want to replace the source. Apple’s Preview guide

The filter is the quick built-in reduction option; it does not offer a named target size or a readable-quality slider in the documented Preview workflow. Don’t expect to enter a value such as “under 5 MB” or specify a particular image resolution through this menu. The exported size depends on the content and options, so check the actual result before sending or archiving it.

Inspect the exported PDF before using it

Open the new copy in Preview. Compare the pages you checked before exporting, at the same zoom level. Look for fuzzy small text, blocky photographs, faint or broken lines, and details that have become hard to distinguish. Read a paragraph at the size you normally use, then zoom into fine-print areas. If the document will be printed, review the parts that need to survive on paper as well as on screen.

If the compressed version remains clear enough for its intended use, check its file size in Finder and use that copy. If quality has fallen too far, return to the original rather than compressing the already-compressed copy again. Repeating a lossy export can compound visible degradation, especially in image-heavy pages; treating the original as your starting point preserves a clean fallback. This is a cautious workflow recommendation based on Apple’s warning that compression may reduce quality, not a guarantee about how a particular file will behave.

Use the export checkboxes only for the purpose they serve

Apple also documents three checkboxes in Preview’s PDF export options: Create Linearized PDF, Optimize images for screen, and Save images as JPEG. The first is described as optimizing a PDF for fast loading and viewing in web browsers. The second is described as optimizing images for screen viewing to reduce file size. The third converts images to JPEG, which uses image compression. Apple’s Preview guide

Those descriptions do not mean each setting preserves the same visual quality or is suitable for every file. Linearization is about browser loading and viewing, so it is not itself a promise of smaller output or sharper pages. Screen optimization is intended for screen viewing; consider whether your use is limited to screens before relying on it. JPEG compression applies to images, so compare photographs, scans, and fine image detail after export. Do not assume text, charts, or every page will be affected in the same way.

The available controls can vary with the export format and macOS version. If you do not see a documented checkbox or menu item in your Preview export dialog, don’t infer that an equivalent option is hidden behind a particular command. Apple’s Preview guide documents the choices above, and its general export guide explains that the Format menu selects the file type and that size-reduction options are available. Apple’s export guide

If the result is still too large

First check whether your goal is smaller storage or faster web viewing: they are not identical. The Create Linearized PDF option is documented for faster loading and viewing in browsers, while Optimize images for screen is described as a way to reduce size by optimizing images for screen use. Use the latter only if its screen-oriented tradeoff fits the PDF’s purpose, and inspect the output as above. Apple’s Preview guide

If Preview’s filter creates a file that is too large or too degraded for your needs, Preview’s documented controls may not provide the exact size-versus-quality adjustment you want. Keep the original, and choose another PDF tool only if it clearly provides the controls and format handling your task requires. For any tool, compare its output before replacing the original. If you need a reduction to meet a strict upload limit, measure the exported file in Finder and confirm the recipient accepts that file; Preview does not document a guaranteed target-size feature in this workflow.

Apple also documents a separate approach in ColorSync Utility: open the PDF, choose a Quartz filter, preview its effect, and click Apply to save changes. Because this alters a PDF through a filter, use a copy and review the result rather than assuming it preserves quality. Apple’s ColorSync Utility guide

A simple readability-first decision sequence

Use this sequence when the first export does not give you an obvious answer:

  1. Keep the original untouched and export one reduced copy.
  2. Compare the smallest text, finest lines, and most detailed image against the original at the same zoom.
  3. If it remains readable for the intended use, verify the new file size and use the copy.
  4. If it fails the visual check, discard that copy and start again from the original. Try the documented screen-image option only when on-screen viewing is the goal, then inspect again.
  5. If neither version meets both the size requirement and readability needs, Preview’s documented controls may not be enough for that particular PDF. Avoid repeatedly compressing the already-reduced copy.

This method does not promise a particular file-size reduction: Apple says the result varies with selected options. The useful outcome is a verified copy that meets your size requirement without losing details your reader needs. If you use Wallo to organize open Mac windows and to-dos around this task, it can help keep the PDF and related work in view; PDF compression itself happens in Preview.

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