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

A PDF shrinks most when it contains images, because images take up far more space than text. If your PDF is mostly words, compression won't help much — the file is already small. If it's mostly photos or scans, you can usually cut the file size in half or more by reducing image quality or resolution.

The method you choose depends on what you're compressing for. Emailing a document? Reducing image quality works fine. Archiving something you might need to read closely later? You'll want to keep higher quality. Most people can compress a PDF using free tools built into their operating system or through online converters, without installing anything new.

Key Takeaways

  • PDFs compress best when they contain images; text-heavy PDFs won't shrink much because text already takes very little space.
  • Your operating system likely has a built-in tool: macOS has Preview, Windows has Microsoft Print to PDF, and Linux has command-line options like Ghostscript.
  • Online PDF compressors work in your web browser and don't require installation, but you're uploading your file to someone else's server.
  • Reducing image resolution (DPI) shrinks file size the most, but lower resolution means blurrier images if you zoom in or print.
  • You can also compress by removing pages, flattening form fields, or deleting embedded fonts if the PDF doesn't need to look identical on every device.

Compress a PDF on macOS using Preview

macOS includes Preview, which can compress PDFs without extra software. Open the PDF in Preview, go to File and select Export. In the dialog that appears, change the format dropdown from "PDF" to "PDF" (it stays the same), then look for a Quartz Filter dropdown menu. Select Reduce File Size.

This method works best for PDFs with images. Preview will lower the image resolution automatically. The tradeoff is that images become less sharp, especially if someone zooms in or prints the document. If you need to keep image quality high, skip this and try a different method. Click Save and Preview will create a new, smaller PDF file.

Compress a PDF on Windows using Print to PDF

Windows doesn't have a built-in compression tool like macOS, but you can use the Print to PDF feature to reduce file size. Open the PDF in any program that can read it — Adobe Reader, Microsoft Edge, or even Chrome. Go to File and select Print. In the printer dropdown, choose Print to PDF.

Before you print, look for a Properties or Preferences button in the print dialog. Set the quality to Draft or Low instead of Best or High. This tells Windows to compress images as it creates the new PDF. Click Print, choose where to save the file, and Windows will create a compressed version. The result is usually 30 to 50 percent smaller, though images will be noticeably lower quality.

Use an online PDF compressor for quick results

Online tools like Smallpdf, ILovePDF, or PDF Compressor let you upload a PDF, compress it, and read the result without installing software. Go to the website, click the upload button, select your PDF, and the tool compresses it automatically. Most let you choose a compression level — Low keeps more quality, High makes the file smaller.

The main drawback is that you're sending your file to someone else's server. If the PDF contains sensitive information, this may not be acceptable. Most reputable services delete files after a few hours, but read their privacy policy first. These tools work well for one-off compressions, especially if you're on a device where you don't want to install new software.

Compress using Ghostscript if you need fine control

Ghostscript is free software that gives you precise control over compression settings. It runs on Windows, macOS, and Linux. read it from the official Ghostscript website, then open a terminal or command prompt and use a command like this:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

Replace input.pdf with your file name and output.pdf with what you want to call the compressed version. The -dPDFSETTINGS option controls quality: use /screen for the smallest file (lowest quality), /ebook for medium compression, or /printer to keep higher quality. This method works best if you're comfortable using the command line and need to compress many PDFs the same way.

Reduce file size by removing unnecessary content

Sometimes the fastest way to shrink a PDF is to remove pages or elements you don't need. If you're emailing a 50-page document but only need pages 1 through 10, delete the rest. Use free tools like PDFtk, Preview on macOS, or online editors to remove pages, then save the result.

You can also flatten form fields if the PDF contains interactive forms you've already filled out. Flattening converts the form into regular text and images, which takes less space. Some PDFs also contain embedded fonts that aren't needed if the document will only be read on screen. Removing these saves a few kilobytes, though it's rarely the main source of file bloat.

Understand the quality versus size tradeoff

Every compression method involves a choice between file size and quality. Lowering image resolution from 300 DPI (dots per inch) to 72 DPI cuts file size dramatically, but the images look pixelated if you zoom in or print. For documents you're emailing or posting online, 72 to 96 DPI is fine. For documents you might print or archive, keep 150 DPI or higher.

Text in PDFs almost never needs compression — it's already tiny. The size comes from images, so focus compression there. If a PDF is still large after you've compressed images, check whether it contains embedded videos, audio, or high-resolution graphics. Those are harder to compress without specialized tools.

Frequently Asked Questions

Will compressing a PDF make it unreadable?

No, but it may look worse. Compression lowers image quality, so text and photos become less sharp. For most uses — email, web viewing, screen reading — this is invisible. If you need to print the document or zoom in closely, you'll notice the difference. Always keep the original file if you might need high quality later.

How much smaller can I make a PDF?

It depends entirely on what's in it. A text-only PDF might shrink 10 to 20 percent. A PDF full of high-resolution photos can shrink 50 to 80 percent. The more images and the higher their original resolution, the more you can compress. Try compressing a copy first to see the result before you delete the original.

Can I compress a PDF that's password-protected?

Most compression tools won't work on password-protected PDFs unless you remove the password first. If you own the PDF, open it in Adobe Reader or Preview, remove the password through the security settings, then compress. If you don't own it, you'll need permission from whoever set the password.

Is it safe to use online PDF compressors?

Reputable services like Smallpdf and ILovePDF use encryption and delete files after a few hours. However, you are uploading your file to their server. If the PDF contains confidential information, use a local tool instead — Preview on macOS, Print to PDF on Windows, or Ghostscript on any system.

What if compression doesn't make the file small enough?

Try removing pages you don't need, converting the PDF to an image format like JPG if it's mostly pictures, or splitting it into multiple smaller PDFs. If the file is still large, the PDF may contain embedded media like video or audio, which requires different tools to remove.