How to compress a PDF offline

To compress a PDF without internet, open Compress PDF once while you are online and wait a few seconds. The page saves itself on your device. Later, with no connection, open the same page, choose the PDF, pick a size and select Compress PDF →. Nothing has to be downloaded or sent.

Why it works without a connection

The compression code runs in your browser, not on a server. On your first visit the browser stores the page and its code, so it can open again without a network. This is useful on a bus, in a building with no signal, or when mobile data is expensive, and it shows that your file is not uploaded.

Step 1: save the page while online

Open Compress PDF and wait a few seconds.
For quicker access, add the site to your home screen. On iPhone, tap Share in Safari, then Add to Home Screen (Apple’s steps). On Android, tap Install app at the bottom of the page if it appears, or use the install option in Chrome’s menu (Chrome Help).

The other tools are saved the same way. Opening each tool you plan to use once while online is the surest way to have it ready.

Step 2: compress while offline

Open the saved page or the home screen icon.
Select Choose a PDF, or drag the file onto the box. Files can be up to 30 MB.
Pick a compression mode. Optimize — keep page content keeps text selectable. Image-based — for scans and photos shrinks scanned pages. Target size — for upload limits aims for a size you choose.
For a target, choose one of 20 KB, 50 KB, 100 KB, 200 KB, 300 KB, 500 KB, 1 MB or 2 MB, or Custom and type a number in Custom size in KB.
Select Compress PDF →, then Download result ↓.

In our test on November 2, 2026, we opened the page, turned the connection off, and compressed a 1.90 MB one-page passport scan with a 500 KB target. The result was 286.6 KB in Chrome on Android and 286.1 KB in Safari on iPhone, 85% smaller in both.

Which mode to choose

A form or letter typed on a computer: start with Optimize. These files are often small already, and Optimize keeps the text sharp and searchable.
A scan or phone photo: Image-based or a target size. Pages become pictures at a lower resolution, so the text can’t be selected afterwards.
A portal with a limit: Target size. The tool counts 1 KB as 1,000 bytes so the file fits whichever way the portal counts. If color won’t fit, tick Use grayscale if color won’t fit.

What needs one online visit first

Compress PDF itself needs nothing extra. A few features in other tools are saved only after their first use: the decoder for iPhone HEIC photos in Scan to PDF and Resize photo in KB, and the text recognition data for each language. If you try them offline before using them once online, the page shows an error instead of sending anything.

If it doesn’t work

The page won’t open offline. It wasn’t saved yet. Open it once more while online and wait until it finishes loading. A private or incognito window may not keep the saved copy.
The file didn’t get smaller. Some PDFs are already compressed. The tool keeps the original rather than give you a bigger file. Read why a PDF won’t get smaller.
The target can’t be reached. Very long files can’t fit a tiny target. Remove pages you don’t need with Split PDF, then try again.