Upload portals often cap files at 2, 5, or 10 MB, and a scanned document can easily be 30 MB or more. Before you upload it to a compression website, try the tools already on your Mac.
Why is my PDF so large?
- Scanned pages. Each page is a full image. A 20-page scan at 600 DPI adds up quickly.
- High-resolution photos. Images placed in a document keep their original size unless they were compressed first.
- Embedded fonts. Usually a small share, but noticeable in short documents.
Because images are nearly always the cause, the same rules apply as when you compress images on Mac: lower the resolution and use JPEG compression.
Method 1: Preview's Reduce File Size filter
- Open the PDF in Preview.
- Choose File → Export.
- Open the Quartz Filter menu and choose Reduce File Size.
- Give the file a new name so you keep the original, then click Save.
This often cuts the size dramatically, but it can also make scanned text soft or hard to read. Always open the result and zoom in before you send it.
Method 2: A sharper custom filter with ColorSync Utility
If the built-in filter is too blurry, create a gentler one:
- Open ColorSync Utility (in Applications → Utilities) and click Filters.
- Find Reduce File Size, click the menu arrow beside it, and choose Duplicate Filter.
- In the copy, open Image Sampling and set a larger size or a resolution of around 150 DPI. Under Image Compression, raise the quality.
- Rename the filter. Custom filters saved in your user Filters folder (
~/Library/Filters) show up in Preview's Quartz Filter menu.
150 DPI keeps typed text readable while still shrinking scanned pages a lot.
Method 3: Split the PDF into smaller parts
Some portals accept several files. In Preview, show thumbnails with View → Thumbnails, select a range of pages, and drag them to the desktop to create a new PDF with just those pages.
Going the other way? Here's how to merge PDFs on Mac.
Method 4: Compress PDFs from the right-click menu
FinderBuddy puts Compress PDF in Finder's right-click menu, next to split, merge, and extract pages. Select one PDF or several and compress them in one step, without opening Preview or a website.
It all runs on your Mac. One payment covers lifetime updates.
Frequently asked questions
- How do I compress a PDF on Mac for free?
- Open it in Preview, choose File → Export, and set Quartz Filter to Reduce File Size. Save it under a new name so you keep the original.
- Why is my PDF blurry after using Reduce File Size?
- Preview's built-in filter downsamples images heavily. Create a custom filter in ColorSync Utility with a higher resolution (around 150 DPI) and quality for sharper results.
- Does reducing PDF size remove text or links?
- No. Compression mostly affects images. Typed text, links, and form fields usually stay the same.
- How can I get a PDF under 2 MB?
- Compress it with a Quartz filter first. If it's still too large, split it into parts or rescan the pages at 150 DPI in grayscale.