How to reduce a PDF’s size on your phone for email and upload limits

Why the PDF on your phone is so big

Open a heavy PDF and look at what is in it. A contract scanned at the office, a brochure exported for a print shop, a report with phone photos pasted in: each page carries one or more pictures, often at 300 dots per inch or more, which is what a printer wants. A phone screen or a laptop shows an A4 page at roughly 150 to 200 dots per inch. Everything above that is weight you send and the reader never sees.

Text costs almost nothing by comparison. A page of typed words is a few kilobytes of letters and a font, so a PDF made of text alone is already small. That gives the rule for shrinking any PDF: make the pictures smaller and leave the text alone. Done that way, the words stay sharp at any zoom and can still be selected, searched and copied, and the links and form fields keep working.

What the phone can do by itself

We tried the iPhone’s own options on iOS 27, in Apple’s iPhone simulator, on real PDFs.

In the Files app, select a PDF (the More button, then Select), tap More at the bottom, and you find Compress. It packs the file into a ZIP archive next to it and leaves the PDF inside exactly as it was: our 252 KB PDF became a 238 KB ZIP holding the same PDF. Most upload forms refuse a ZIP, and the person who receives it has to unpack it before they can read anything.

Under More › Quick Actions there is also Optimize File Size, which writes a copy with “Compressed” added to its name. On a 12 MB brochure full of photos the copy came out less than 1% smaller, and on a 2 MB scan almost exactly the same size. It costs one tap to try, and on your file it may do better, but do not count on it for a 200 KB limit.

On Android, what you have depends on the apps your phone maker installs, which differ between a Samsung, a Pixel and the rest, and we have not tested them. The steps below work the same in Chrome on any Android phone as in Safari on an iPhone.

The steps in Safari or Chrome

Compress PDF on this site reduces the size in the mobile browser you already have: the PDF is read, its pictures are shrunk and the new file is written on your phone, and nothing is uploaded.

1. Open Compress PDF and tap Choose PDFs to compress. Pick the file from Files on an iPhone, or from your downloads or Drive on Android. You can pick several.
2. Under How small?, choose one of the three settings; the table below says which suits your file.
3. Tap Compress PDF. A bar counts the pictures as they are shrunk.
4. The result shows the new size against the old one, and how many pictures were shrunk. Tap Save to Files or share on an iPhone to keep it or attach it to an email; on Android the card offers Save as… and Download.

On the same 12 MB brochure, Recommended in Safari brought the file down to about a third of its size, with the text still selectable. If the result is still too big, the page says so and suggests the next setting to try.

When a form says 200 KB or 1 MB

Job portals, visa forms and university applications often set a hard limit and reject anything over it. Choose Size in KB, then tap 100, 200, 500 or 1000 (that is 1 MB, by either count), or type your own limit from 20 to 50,000 KB. The button changes to say what it will do, such as Compress to 500 KB.

The tool then tries settings from gentle to strong and stops at the first one that fits, so you get the best quality that is still under the limit. Some PDFs cannot get there by shrinking pictures alone. For those, a box under the limit, on unless you untick it, lets the tool turn whole pages into pictures, which is how scanner apps reach very small sizes. The price is that the text on those pages can no longer be selected or searched, and they may come out in grey. The result tells you when that happened.

If even that cannot reach the limit, the page keeps the version with selectable text and says how close it got. When a pictures-only version is smaller, a quiet button offers it, with its size, and you choose.

The pages for compressing a PDF to 200 KB and to 1 MB open with the limit already set.

When nothing gets smaller

Some PDFs barely move, and the result says why:

• No large pictures. A PDF exported from Word or a web page is mostly text, fonts and drawings, which this tool keeps as they are. It is already near its smallest.
• Scans stored a special way. Scans from office scanners are often stored as JPEG 2000, JBIG2 or CCITT pictures, which are already very compact and are kept as they are. Size in KB with pages turned into pictures can still go smaller, at a lower quality and without selectable text.
• Pictures already compressed. If someone compressed the PDF before you, a second pass at the same setting finds nothing left to remove. Strong or a size in KB may still help.

If you made the PDF yourself from photos, the better fix is often upstream: make the PDF again with smaller pictures. JPG to PDF has a file size limit for that, and Scan to PDF has B&W pages and a Smaller file option.

Which setting to choose

Setting	What it changes	Choose it when	Text still selectable
Recommended	Pictures down to about 190 dots per inch on A4, good-quality JPEG	Email, upload, reading on any screen	Yes
Strong	Pictures down to about 130 dots per inch	Reading on a screen only, never printing	Yes
Size in KB	The best setting that fits your limit, gentlest first	A form gives a number	Yes, unless pages had to become pictures

Keep the original either way. A compressed copy is for sending; the full-size file is the one to print, archive or compress again later with a different setting.