The fastest way to compress a PDF on Mac
The built-in Preview app on your Mac can reduce a PDF's file size without needing to download anything. Open the PDF in Preview, go to File > Export, choose your save location, then click the Quartz Filter dropdown and select Reduce File Size. Save the file with a new name. The compressed version will be noticeably smaller, though image quality drops slightly.
If you work with PDFs regularly or need more control over compression, the Mac App Store has paid options like PDF Squeezer and Compressor that let you choose compression levels. For occasional use, Preview is free and built in — you do not need to install anything.
Key Takeaways
- Preview's Reduce File Size filter compresses PDFs without installing software, though it reduces image quality noticeably.
- Dragging a PDF into Mail and using the attachment compression option works if you are already composing an email.
- Third-party Mac App Store apps like PDF Squeezer give you control over compression level and are worth the cost if you compress PDFs weekly.
- Online tools exist but require uploading your PDF to a server, which is a security risk if the document contains sensitive information.
Using Preview's built-in compression
Preview is the simplest route because it comes with every Mac. Open your PDF in Preview (right-click the file, select Open With, then Preview). Go to the menu bar and click File, then Export. A save dialog opens.
Near the bottom of the dialog, you will see a dropdown labeled Quartz Filter. Click it and select Reduce File Size. Choose where to save the compressed file — give it a new name so you keep the original. Click Save. The compressed PDF will be 30 to 50 percent smaller than the original, depending on what the PDF contains.
The trade-off is image quality. Photos and graphics become noticeably softer. Text stays readable. If your PDF is mostly text with a few images, this method works well. If it is a photo-heavy document or design file, the loss may be too much.
Compressing a PDF through Mail
If you are sending the PDF by email anyway, Mail can compress it during attachment. Start a new email in the Mail app and click the attachment button (or drag the PDF into the message). Right-click the attachment and select Compress. Mail will reduce the file size before sending.
This method is convenient if compression is a one-time need for a specific email. The compression is automatic and you do not have to save a separate file. However, you cannot control how much compression happens, and the recipient gets the compressed version — you cannot keep a full-quality copy for yourself without doing the work twice.
Third-party apps from the Mac App Store
PDF Squeezer and Compressor are paid apps available in the Mac App Store that give you more control than Preview. Both let you choose compression levels — you can prioritize file size or image quality depending on what you need. They also handle batch compression, meaning you can compress multiple PDFs at once instead of one at a time.
These apps cost between $5 and $15 and are worth the expense if you compress PDFs more than once a month. They are faster than Preview for large files and give you a preview of the compressed result before you save. If compression is occasional, Preview is sufficient and costs nothing.
Why online PDF compressors are risky
Websites that compress PDFs for free exist, but they require uploading your file to their server. If your PDF contains financial records, medical information, legal documents, or anything confidential, uploading it to a third-party website creates a security risk. The site may store your file, log your data, or sell access to it.
Mac's built-in tools and App Store apps keep your files on your computer. They do not send anything to the internet. For sensitive documents, this is a significant advantage. For public documents or files you do not mind sharing, online tools work, but the risk is not worth the convenience.
When compression does not work well
Compression works by removing redundant data and lowering image resolution. If your PDF is already compressed — many PDFs from professional sources are — running compression again will not reduce the file size much. You will see little change and may lose quality for no gain.
PDFs that are mostly text compress well. PDFs with high-resolution photos, scans, or graphics compress less effectively because the image data is what takes up space. If you need to send a large scanned document, compression may not be the answer — splitting it into multiple files or asking the sender for a different format might work better.
Frequently Asked Questions
Will compressing a PDF make it unreadable?
No. Text stays readable even after compression. Images and graphics become softer and less detailed, but you can still see them. If the PDF is mostly text, you will barely notice the difference. If it is photo-heavy, the quality drop is visible.
Can I compress a PDF that is password-protected?
Preview and most Mac apps can compress a password-protected PDF if you can open it in Preview. If the PDF is locked against editing, you may not be able to export it. Try opening it first — if Preview opens it, compression will work.
Does compressing a PDF change the original file?
No, if you save it with a new name. Preview and other apps let you choose a new filename during export, which keeps your original untouched. If you save over the original filename, the original is replaced.
How much smaller will my PDF get after compression?
It depends on what the PDF contains. Text-heavy PDFs shrink 30 to 50 percent. Image-heavy PDFs shrink 10 to 30 percent. Some PDFs that are already compressed will not shrink noticeably. There is no way to know until you try.
Is there a way to compress a PDF without losing image quality?
Not significantly. Compression works by reducing image resolution and removing data. You can choose apps that let you set compression levels — lower compression means less quality loss but smaller file size gains. Preview's Reduce File Size filter does not give you this choice.