Shrink a PDF from your phone's browser

A 24 MB tenancy scan and a 2 MB upload box

Ana has just signed a 12-page tenancy agreement at the letting office and scanned it with her phone's camera app on the bus home. The scan is sharp, in full colour, and weighs 24 MB. The council's housing portal wants a copy before Friday, and its upload box says 2 MB at most. Her laptop is at her parents' place for the week.

She does not need it. A phone browser can run the same compression a desktop browser does, as long as the file is a sensible length and the tab stays in front while it works. The steps below are what she does, on the bus, in about the time it takes to read them.

Compressing on the phone, step by step

1. Open Compress PDF in Safari, Chrome or whichever browser you use.
2. Tap Choose a PDF. On an iPhone the Files picker opens, which also reaches iCloud Drive and other connected storage. On Android the system document picker opens.
3. Tap the 2 MB preset, or type an exact size in the target field and switch between KB and MB. For a portal limit, a slightly lower number such as 1.9 MB leaves a safety margin.
4. Press Compress and keep the browser in front with the screen on until it finishes. Switching to another app can pause the tab, and a phone short on memory may reload it.
5. Read the verdict: new size, how much was saved, and the preview beside the original. Look closely at a page with small print to make sure it still reads.
6. Tap Download PDF. The new file keeps your file name with "-compressed" added, so it is easy to tell apart from the scan.

Where the file comes from and where it lands

The trickiest part on a phone is usually finding files, not compressing them. This is where to look on each system; exact folder names can vary with settings and phone maker.

What a phone handles less comfortably

The engine is identical on every device, but a phone gives each browser tab less memory and fewer processor cores than a laptop. Mobile browsers also close tabs that ask for too much memory, sometimes without a warning. There is no measured page ceiling for this tool on phones, because the budget changes with the handset, the browser and what else is open.

In practice, a scan of a dozen pages like Ana's is the comfortable case. A few hundred pages on an older phone is the case to move to a computer. If you do try a long file on the phone, close other tabs and apps first, plug in the charger, and keep the original until you have checked the result.

Phone pitfalls and how to get past them

• The page reloaded and the result vanished. The tab was probably pushed out of memory while you were in another app. Run it again and stay in the browser until the download appears.
• Low power mode makes everything slow. Battery savers throttle the processor. Turn the mode off for the length of the run, or accept a longer wait.
• Attaching the old file by accident. Pickers often sort by date, and the original and the compressed copy sit side by side. Look for "-compressed" in the name before you upload.
• Mixing up KB and MB. A target of 2 KB instead of 2 MB asks for something no scan can reach. Check the unit next to the number.
• Scanning heavier than needed. Many scanner apps have a quality or size setting. A lower setting for text pages saves the compression step next time; the phone scanning guide covers the options.

When to wait for a computer, or skip compression

Wait for a laptop when the file runs to hundreds of pages, when the phone is old and short on memory, or when you need to rework the document first, for example removing pages or rebuilding it from the original source. A computer also makes it easier to check fine print at full size before sending.

Sometimes compression is not the answer at all. If the person who sent you the file can export a lighter version, that copy will often be cleaner than anything squeezed down afterwards. If the file will not open on the phone in the first place, sort that out before anything else with the guide to PDFs that will not open on a phone. And when you want to understand what is making a document heavy, the guide to reducing PDF size walks through it.