How do I compress a PDF on a Mac without blurry pages?

You need to email a PDF or upload it to a portal, it is too big, and the obvious tool on a Mac is Preview. You choose File > Export, pick Reduce File Size from the Quartz Filter menu, and the file comes out small, with pages that look like they went through an old fax machine. Sometimes it even gets bigger.

Your Mac is not misbehaving. That is how the filter works.

Why Preview's Reduce File Size goes too far

Reduce File Size is a fixed recipe applied to every picture in the document. There is no level to choose, and it does not know what your file is for. It shrinks and recompresses images hard, whether they are photos, scanned letters or charts.

That causes three familiar problems:

• Scanned pages go blurry. In a scan the words are part of the picture, so shrinking the picture shrinks the words with it.
• Photos get blocky patches around edges and in smooth areas like sky.
• Some files grow. A PDF that was already efficient, or is mostly text, can come out larger after the filter rebuilds it.

None of this shows until you open the result, so check it every time.

A smaller PDF that still looks right

Compress PDF runs in Safari, Chrome or any other browser on your Mac, with nothing to install. The difference from Preview is control:

Text and line art are not pictures, so they stay sharp at every level. Only the photos and scans inside the file are made smaller.

Step by step

1. Open Compress PDF and drag the file from Finder onto the upload panel.
2. Choose a level. Start with Recommended; it suits most files.
3. If a form or mail system gave you a limit, choose To a size instead and pick 100 KB, 200 KB, 500 KB or 1 MB, or type the limit in KB.
4. Compress, then download. Your Mac puts the file in Downloads, with -compressed added to its name.
5. Open it in Preview and zoom in on the smallest text before you send it.

The result screen shows the size before and after. If the file was already about as small as it gets, it says so rather than handing you a worse copy, and if compressing would make it larger, it tells you to keep your original.

Typing a limit in KB

The size box counts 1 KB as 1,000 bytes, so typing the limit as whole thousands is always safe: 2000 for 2 MB, 5000 for 5 MB, 10000 for 10 MB. A file that fits that number fits on sites that count a megabyte either way. For the two most common limits there are pages that open already set: Compress PDF to 1 MB and Compress PDF to 2 MB.

What actually makes a PDF big

Knowing this tells you how much compression can do before you start.

• Scans and phone photos of paper are almost entirely pictures. They shrink a lot, often to a fraction of their size, and usually stay perfectly readable at Recommended.
• Documents with photos, like brochures and reports, shrink a good deal.
• Text documents exported from Pages or Word are already small. Compression may take off a few percent, or nothing.

If yours is the third kind and still too big, the size is genuine content. The fix is fewer pages, not harder compression: SmartShrink fits the content of mostly empty pages onto fewer sheets, and splitting the document into parts works when the limit is per file.

Two quick wins before you compress

Take out pages nobody needs. Preview is good at this. Show the sidebar with View > Thumbnails, select the pages you want gone (hold Command to pick several), press Delete, and save. A form that only wants your signed page does not need the eleven pages of terms in front of it, and every page you remove is weight you do not have to compress.

Go back to the original if you have it. If the PDF came from a Pages, Keynote or Word file with large photos in it, exporting again from that file and then compressing gives a cleaner result than compressing a PDF that has already been squeezed once. Compression works best on the first generation of a file, not on a copy of a copy.

Can Preview do better?

There is a way, if you like tinkering. Open ColorSync Utility (in Applications > Utilities), go to its Filters, duplicate the Reduce File Size filter and change its image settings so it keeps more resolution. Filters you save there appear in Preview's export menu. It works, but you are guessing at numbers, and you still cannot say "make it fit under 2 MB". For an occasional file, a tool with levels and a size target is quicker.

Forms and privacy

A fillable form stays fillable after compressing; its fields are carried across. The pages, the layout and the text are left as they were, because only the pictures change.

The file is sent over an encrypted connection to our server, compressed there, and deleted after processing. Nothing is installed on your Mac and no account is needed.

A routine that works

1. Compress at Recommended.
2. Still too big? Use To a size with the exact limit.
3. Still too big? It is the page count, not the pictures. Remove the pages you do not need, fit sparse pages onto fewer sheets, or split the file.
4. Open the result and read the smallest text before sending.