How to Compress a PDF Without Losing Quality
A PDF that is too big to email or upload is one of the most common small frustrations of office life. The good news is that most oversized PDFs can be shrunk dramatically with no visible change, once you understand what is making them large.
Written by the Toolseza team · Updated 2026-10-01
Why PDF files get large
A PDF holds text, fonts, images and page descriptions. Text is tiny: a page of plain text is usually only a few kilobytes. Images are the problem. A scanned page stored as a high-resolution picture can be one or two megabytes on its own, so a 20-page scan easily passes 30 MB. Embedded fonts, duplicated images and leftover editing data add more.
This explains why compressing a text-only report often saves very little, while compressing a scanned contract can cut it by 80 percent or more.
What compression actually does
Compression tools mainly work on the images. They lower the resolution, for example from 300 pixels per inch to 150, and apply stronger JPEG compression. They may also strip duplicate resources and unused metadata. Reading on a screen rarely needs more than 150 pixels per inch, so the change is hard to notice.
The trade-off is detail. If the document will be printed, or contains fine print and diagrams, choose a gentler setting, or keep both versions: a small one for sending and the original for the archive.
A simple step-by-step approach
First, decide the purpose. For email, aim for under 10 MB, since many providers cap attachments around 20 to 25 MB once encoding overhead is included. For web upload, check the form for its limit.
Second, compress with a medium setting and compare the size and the look. Zoom in on small text and on any stamps or signatures. If it is still readable, you are done. If the file is still too big, split it into parts or compress the images separately before you rebuild the PDF.
Third, keep the original untouched. Compression is lossy for images, so you cannot restore detail later.
Tips for scanning smaller PDFs in the first place
Scan at 150 to 200 pixels per inch in grayscale rather than colour for plain text documents, and use black-and-white mode for pages with no pictures. Crop off the surrounding table or background. A well-scanned page can be under 100 KB, which is far smaller than the same page photographed in colour at full resolution.
A note on privacy
Contracts, IDs and financial statements are sensitive. Prefer a tool that processes the file on your own device rather than uploading it. The Toolseza PDF compressor works in your browser, so the document is not sent to our servers.