The fastest way to compress a PDF depends on what's inside it

If your PDF is mostly text, you can shrink it to 10–20% of its original size using free tools. If it's full of photos, you'll get smaller results — usually 30–50% — because photos contain far more data than words. The method that works best depends on whether you're compressing on Windows, Mac, or online, and whether the PDF has images, scans, or just text.

Start by checking what's actually taking up space. Right-click the PDF file, select Properties (Windows) or Get Info (Mac), and note the current size in megabytes. After you compress it, you'll see exactly how much smaller it got. This tells you whether the tool worked well enough for what you need.

Key Takeaways

  • PDFs with photos compress much more than PDFs with only text, because images hold the most data.
  • Built-in tools on Windows and Mac can compress PDFs without installing anything new — Preview on Mac and Print to PDF on Windows both work.
  • Online tools like Smallpdf, ILovePDF, and PDF Compressor work in your web browser and don't require software installation.
  • Reducing image quality inside the PDF shrinks file size the most, but you lose sharpness — test on a copy first to see if the result is acceptable.
  • Password-protected PDFs usually cannot be compressed by online tools, so you'll need desktop software or to remove the password first.

Using Preview on Mac to compress a PDF

Preview is built into every Mac and can compress PDFs without any extra software. Open the PDF in Preview, go to File menu, then select Export. A dialog box appears with options at the bottom.

Look for the dropdown that says "Quartz Filter" and select "Reduce File Size" from the list. This automatically lowers the quality of images inside the PDF to make the file smaller. Click Save, and Preview creates a new compressed version. The original stays unchanged. Test the compressed version by opening it — if text is still sharp and photos are acceptable, you're done. If it looks too blurry, go back and try exporting without the filter, or use a different tool.

Compressing a PDF on Windows using Print to PDF

Windows doesn't have a built-in compression tool like Preview, but you can use the Print to PDF feature to shrink files. Open the PDF in any program that can read it — Microsoft Edge, Adobe Reader, or even File Explorer. Press Ctrl+P to open Print, then change the printer to "Print to PDF" or "Microsoft Print to PDF".

Before you print, look for a Properties or Preferences button and set the quality to "Draft" or "Low Quality" instead of the default. This tells Windows to compress images as it creates the new PDF. Click Print, choose where to save the new file, and Windows creates a smaller version. Like the Mac method, this works best on PDFs with images. Text-only PDFs may not shrink much because there's little to compress.

Online tools that work in your browser

If you don't want to install software, several free websites compress PDFs directly in your browser. Smallpdf.com, ILovePDF.com, and PDF Compressor (pdfcompressor.com) all work the same way: you upload your PDF, the site compresses it, and you download the result. No account is required for basic compression on any of these.

Upload your file, wait a few seconds while the site processes it, then download the compressed version. These tools work on Windows, Mac, and Linux equally well. One limitation: most online tools cannot compress password-protected PDFs. If your PDF is locked, you'll need to remove the password first using a tool like PDF Unlocker, or use desktop software instead.

Using Adobe Acrobat to compress with more control

Adobe Acrobat (the paid version, not the free Reader) gives you detailed control over compression. Open your PDF in Acrobat, go to File menu, then select Export As, and choose PDF. A dialog appears with compression options.

You can set image quality separately for color images, grayscale images, and monochrome (black and white). Lower quality means smaller file size. Acrobat also lets you remove embedded fonts and metadata, which saves space on some PDFs. After you set your preferences, click Export and choose where to save. This method takes longer than Preview or Print to PDF, but gives you the most precise control over what gets compressed and what stays sharp.

What happens when you compress a PDF, and what you lose

Compression works by reducing image quality inside the PDF. Text stays sharp because text doesn't need much data to display clearly. Photos and scans get blurrier because the compression tool throws away some of the image information to make the file smaller. This is permanent — once you compress a PDF, you cannot undo it and get the original quality back.

Always compress a copy of your PDF, not the original. Keep the original file in case you need the full quality later. After compression, open the new file and check whether photos, charts, or scans still look acceptable for how you plan to use it. If you're emailing the PDF or uploading it to a website, smaller file size matters more than perfect image quality. If you're printing it or need to read small details, you may want to skip compression or use a gentler setting.

When compression doesn't work well

Some PDFs don't compress much no matter what tool you use. This usually means the file is already compressed, or it contains mostly text with very few images. A 50 KB PDF of a one-page letter will stay roughly the same size because there's almost nothing to compress. A 200 MB PDF of 500 scanned pages can often shrink to 50–80 MB because there's so much image data to reduce.

If you're trying to compress a PDF that's already small, the effort may not be worth it. If you're trying to compress a very large file and the results are disappointing, the PDF may have been created in a way that resists compression. In that case, your options are limited: accept the larger file size, or recreate the PDF from the original source (like re-scanning documents at lower resolution, or re-exporting from the original software).

Frequently Asked Questions

Will compressing a PDF make it look bad?

Text stays sharp, but photos and scans get blurrier because compression removes image detail. How noticeable this is depends on the original quality and how much you compress. Test on a copy first — if it looks acceptable for your purpose, use it. If not, try a gentler compression setting or skip compression.

Can I compress a password-protected PDF?

Most online tools cannot compress locked PDFs. Desktop tools like Adobe Acrobat can, but they still need the password. If you own the PDF, remove the password first using a tool like PDF Unlocker, then compress it. If you don't own it, you'll need to contact whoever created it.

Does compressing a PDF change the file format?

No, the result is still a PDF. Compression only reduces the data inside the file — it doesn't convert it to a different format like JPG or Word. You can open and use the compressed PDF exactly like the original.

How much smaller will my PDF get after compression?

It depends entirely on what's inside. A PDF with many photos might shrink to 30–50% of its original size. A PDF with mostly text might only shrink 10–20%. Some PDFs that are already compressed won't shrink noticeably at all. Check the file size before and after to see the actual result.

Is it safe to use online PDF compression tools?

Reputable sites like Smallpdf and ILovePDF delete your files from their servers after a few hours. However, if your PDF contains sensitive information, using desktop software like Preview or Adobe Acrobat keeps everything on your computer. Choose based on whether you're comfortable uploading the file to the internet.