How to reduce PDF file size: what actually works

The short answer

To reduce a PDF's size, remove pages you do not need and shrink the images inside it, because images are what make most PDFs large. Some jobs can be done in a browser, and some need desktop software, and we will be honest about which is which. Toolbyte does not have a PDF compressor at the moment, so this guide only recommends our tools where they really help.

First, find out why it is big

A PDF's size depends mostly on its images, not its text. A text document with 20 pages can be well under 1 MB, while the same number of scanned pages can reach 30 MB or more. Check what you have:

• Text exported from Word, Docs or a website: usually small. If it is large, it probably contains big pictures or embedded fonts.
• Scans or phone photos turned into a PDF: large, because every page is a full-size picture.
• Presentation exports: large when the slides contain many high-resolution photos.

If you can select and copy text on the page, it is real text. If you cannot, the page is a picture of text, and that is what to shrink.

Option 1: remove pages you do not need

Taking out pages is the simplest way to cut size, and it loses no quality. If you only need some pages, keep only those. Use Organize PDF to delete pages, or Split PDF to extract a range such as 1-5,8 into a new file. This works because each page carries its own images, so fewer pages means a smaller file. Do this first before anything else.

Option 2: rebuild a scan from smaller images

If your PDF is a scan, you can shrink it by turning its pages back into images, compressing them, and building a new PDF. The steps in the browser are:

1. Open PDF to JPG and export the pages. You get a ZIP of images.
2. Compress each image with compress image, or choose a target such as 200 KB or 100 KB.
3. Put the images back together with JPG to PDF, in the right order.

This can reduce a heavy scan dramatically, but it has trade-offs. The new PDF contains pictures only, so any text that was selectable in the original is no longer searchable. It is fine for forms, receipts and certificates that people only read or print, and a poor choice for documents where search or copying matters. It is also manual for long files, so it is practical for roughly 1 to 20 pages.

If you are starting from phone photos, compress the images first and then make the PDF. Our guide on converting JPG to PDF explains page size and order.

Option 3: export again at lower quality

If you still have the original document, the best fix is to export it again with smaller images. Most programs have a setting for this:

• In Word, use Save As PDF and choose the "Minimum size" option instead of "Standard".
• In any editor, replace very large pictures with smaller versions before exporting.
• In PowerPoint, use Compress Pictures before you export to PDF.
• In Preview on a Mac, Export with the Quartz filter "Reduce File Size", though the result can be too blurry for text, so check it.

The key idea is the same everywhere: smaller or lower-quality images produce a smaller PDF.

Option 4: use desktop software for real recompression

Recompressing the images inside an existing PDF is something a desktop program does best. Tools with an optimise or reduce file size feature, such as the paid Adobe Acrobat or free command-line tools, can lower image resolution and strip unused data without you rebuilding the file. In-browser tools are limited here because they have to work within your device's memory, and the best compression methods need heavier software. We do not offer this yet, and we would rather say so than promise a result we cannot deliver.

What does not help

• Zipping a PDF: PDFs are already compressed, so a ZIP file is usually only a few percent smaller.
• Merging files: it makes a file bigger, not smaller, because the result holds all the pages.
• Renaming or changing the extension: it changes nothing.
• Re-saving repeatedly: it rarely helps, and can degrade images if quality is lowered each time.

Check the result

Open the smaller file and zoom in. Check that text is readable, signatures and stamps are clear, and the page order is right. Then look at the new size in your file manager. If a form or email limit is the reason you are shrinking, compare against that number, not a guess.

Quick decision guide

• Only part of the document is needed: remove pages with Organize PDF.
• It is a short scan and you need to be under a limit: rebuild with smaller images.
• You have the original file: export again at a smaller image quality.
• It is a long, image-heavy PDF: use desktop software that can recompress images.