How to reduce PDF file size

The three things that make a PDF big

A PDF is heavy for one of three reasons. Find yours before you set a number, because the reason decides how much weight comes off.

1. Scanned pages. Every page is a photograph of paper, so the file weighs what the photographs weigh, and the text on them is not text at all.
2. Placed images. A report with eight camera photos in it carries eight camera photos, at a resolution no printer and no screen will ever use.
3. Embedded fonts and leftover structure. A font program usually ships every glyph it was designed with, and a document draws a fraction of them. Overhead from past edits sits in the file uncleaned. This one is real but it is not the whole story on its own.

Tell them apart in five seconds. Open the file and try to select a line of text with the cursor. If the text highlights, the pages are not scans and the weight is in the pictures or the fonts. If nothing highlights, the page is an image and the scan is the file.

What the tool does about each one

The compress tool tries four methods against your file and keeps the smallest result that meets the target - or the smallest verified one, with the distance reported, when nothing meets it. The structural method rebuilds the document into a fresh file, dropping overhead past edits left behind. The image method re-encodes the placed images at 150 dpi and quality 75. The font method subsets each embedded font down to the glyphs the pages actually draw.

The fourth is the raster method, and it is the only one that touches the page itself. It renders each page at 150 dpi and writes the page's own text back first as an invisible layer, so the words stay selectable and searchable even though the picture underneath is now an image. It starts only when no other method reached your number, and it can stop early when its own projection cannot beat a candidate another method already holds.

So there is no single answer to what shrinks a PDF. It depends on which of the three problems your file has - and the verdict names the method that won, so the result teaches you which one yours had.

Type a size, not a quality level

Most tools give you a slider named low, medium and high, which tells you nothing about the file you get. This one takes a number in KB and works toward it. One KB is 1,024 bytes here, so a 200 KB target means the output lands under 204,800 bytes.

If an upload form counts a kilobyte as a flat thousand bytes, its 200,000-byte cap sits 4,800 bytes under this tool's 204,800. When a file that reads as the right size still gets refused, set the target a notch lower - 195 KB instead of 200 - and run it again.

Do it in four moves

1. Open the compress tool in this browser tab.
2. Choose the PDF or drag it onto the page; it opens locally.
3. Type the size from the form, in KB or MB, or leave the box for the fallback.
4. Press Compress, then read the verdict: final size, distance to target, winning method.

How much usually comes off

No honest percentage exists here. A guide that promises a fixed cut on any file is guessing, because document kind decides most of it: photo pages carry adjustable image data with a long travel, while a text file's bytes are fonts and structure with far less spare weight to give back.

The documented pilot behind the parent page ran 19 compressions on 10 locally built documents in September 2026 at the default setting. Exact targets landed on plain-text documents; scans and mixed files settled about 40% smaller no matter the target. That split is an observation from one small corpus on one machine, not a promise - and the tighter your number, the more it depends on typed text rather than scans.

Check the result before you send it

Nothing ships unread. Every squeezed candidate is opened again and its text is compared against the source, and any candidate that lost more than 2% of the non-space characters is thrown away rather than offered to you. A file already under the target returns unchanged, and a source the reader cannot open has no baseline to compare.

That rule is why the file you download is sometimes bigger than the number you asked for. When no method reached the target, you get the smallest file that passed the check plus the size it actually reached, and you decide what to do about the gap: split the document and fit the parts, accept a roomier target when the cap bends, or drop dead pages and run again.

From here, the quality guide covers which methods cost you nothing and which ones cost you detail. The compress hub lists the rest of the cluster, including phones, very large files and merged documents.