Compress a PDF without losing quality?

2026-10-10

The honest answer is: partly. Some things in a PDF don’t change at all when it’s compressed; images do change, and the question is whether you can see it.

What stays exactly the same

Compress PDF only works on images. Everything else is kept as it is:

• Text — still sharp at any zoom, still searchable and selectable.
• Lines, shapes and charts drawn as vectors.
• Links, bookmarks, form fields and their values, page sizes and page order.
• Attached files and the document’s own information (title, author).

After compressing, the new PDF is opened again and compared with the original. If text, pages, links or form fields don’t match, you get no file at all — just a message that it couldn’t be compressed.

What changes: the images

Photos and scanned pages are saved again as JPEGs. Two things make a file smaller: lowering the resolution where it is far above what a screen or printer needs, and storing the pixels more efficiently. Both change the image a little. That is why we never call it “lossless”.

How visible that is depends on the level:

• High quality: differences are very hard to see on a normal page, even zoomed in.
• Balanced: ordinary text and photos look the same at normal size; you may notice softening when zooming far in.
• Smallest file: fine detail can look softer. Choose it to meet a size limit, not for print-quality documents.

Images are never made larger or sharper than they were, and an image is only replaced if the new version is clearly smaller.

When there’s nothing to gain

Many PDFs are already efficient: text-only documents, or files whose images were compressed before. Compress PDF then says the PDF is already well compressed and doesn’t hand you a new file. Making it smaller would only mean making it worse.

Some images are deliberately left alone, such as images in print colors and images with a wide-gamut color profile, because changing them could alter how the page looks. Transparent images keep their transparency: only their color is saved again. The result lists how many images were left unchanged.

A quick check

Compress with Balanced, open the result next to the original and zoom in on the part that matters most — small print, a signature, a photo. If you can’t tell them apart at the size you’ll use, keep the smaller one.