How to compress a PDF on Android

Why PDFs get so big

A PDF is a container. A PDF exported from a word processor is mostly text and fonts, and stays small. A PDF made from a scan or photos is mostly images, one per page, and images are where the megabytes come from. A modern phone camera captures more than ten million pixels per photo; put twenty of those pages in one file and you can easily end up with a PDF that email services, job portals and government upload forms refuse.

The usual culprits are:

• page images stored at a much higher resolution than anyone needs to read them;
• colour images for pages that are really just black text on white paper;
• light image compression, which keeps detail no one will ever see;
• extra pages, such as blank backs of sheets or duplicate scans.

How PDF compression works

Compressing a PDF mostly means re-encoding its images: lowering their resolution to what is still comfortable to read, and storing them with stronger compression. Text-only pages shrink the most. Photos and colour pages shrink too, but there is a point where fine print and signatures start to blur.

That’s the trade-off to keep in mind: compression is not free. The aim is the smallest file that is still perfectly readable, not the smallest file possible. After compressing, always open the result and zoom into the smallest text on the page.

Why not use a website?

Search “compress PDF” and you’ll find plenty of websites that do it for free. They work by uploading your file to their servers. For a menu or a flyer that may be fine. For a bank statement, a tax return, a medical report or a scan of your ID, it means handing a copy of a sensitive document to a company you know nothing about, under a privacy policy you probably didn’t read. Compressing on your phone avoids the question entirely: the file never leaves the device.

Step by step: compress a PDF with Scansy

Scansy’s PDF tools work offline, on your phone.

1. Open the PDF tools in Scansy and choose Compress PDF.
2. Pick the document you want to make smaller.
3. Compress it and save the smaller copy.
4. Check the result. Open it in the built-in PDF viewer and zoom into the finest print. If it’s still readable, you’re done.
5. Share it to email, a messaging app or an upload form.

Other ways to make a PDF smaller

Compression isn’t the only tool. Often the biggest savings come from these:

• Send fewer pages. If the form only needs page 2, split the PDF or extract that page instead of sending all twelve.
• Split a large file into parts. Some portals limit each upload rather than the total; two files under the limit are better than one rejected file.
• Scan text in black & white. For letters, contracts and forms, a black & white scan is much smaller than a colour one and often easier to read.
• Remove duplicates and blank pages before exporting.

If you need to put separate files back together afterwards, merge them into one PDF. See how to scan documents to PDF on Android for scan settings that keep files small from the start.

Typical size limits to aim for

Limits vary, so always check the service you’re sending to. As a rule of thumb:

• Many email services cap attachments at around 20–25 MB for the whole message, and some workplace systems are stricter.
• Job applications and government forms often ask for files of 1–5 MB, sometimes less.
• Messaging apps usually accept larger files, but smaller PDFs send faster on mobile data.

If a form has a strict limit and the compressed file is still too large, send fewer pages or split the document, rather than compressing again until the text becomes unreadable.