PDF too big to send? Four compression methods compared
Email caps attachments at 25MB and chat apps are not much better. I tried four ways of compressing the same 48MB PDF and here is which one is worth it.
Yesterday I sent a proposal to a client and the PDF was 52MB. The mail server rejected it outright, and the chat app spent half a minute spinning. So I sat at my desk and tried four compression methods, and wrote the results down so you do not have to repeat the experiment.
Why a PDF gets so big
Scanned pages, embedded high-resolution images and no font subsetting will do it. Email commonly caps attachments at 25MB, and while chat apps may accept 100MB, large files behave badly on phones and annoy the person downloading them.
Four methods, measured
I used the same 48MB PDF, mostly scanned images, for the comparison (your numbers will differ, but the trend holds).
Method 1: an online tool (recommended)
Open Compress PDF, drop the file in, pick a level, download. TwoThink processes it locally in your browser, so nothing is uploaded. Result: about 12MB at the standard level, with slightly soft text edges but still readable; time: under 20 seconds.
Method 2: Adobe Acrobat Pro
Professional grade, with control over image DPI and the compression algorithm. Result: about 10MB, the best image quality; downside: the subscription is expensive and not everyone has it.
Method 3: a mobile app
A free PDF app with splash-screen ads that wanted a 15-second video before compressing. Result: about 14MB; downside: the file is uploaded to the cloud, which I am not comfortable with for confidential documents.
Method 4: Ghostscript on the command line
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook ...
Result: about 9MB; downside: you have to set up an environment, and colleagues will not manage it.
How they compare
| Method | Size | Quality | Privacy | Difficulty |
|---|---|---|---|---|
| TwoThink online | ★★★★ | ★★★ | ★★★★★ | Very easy |
| Acrobat | ★★★★★ | ★★★★★ | ★★★★ | Moderate |
| Mobile app | ★★★ | ★★★ | ★★ | Easy |
| Command line | ★★★★★ | ★★★★ | ★★★★★ | Hard |
Which one to pick
- Sending the occasional file: just use Compress PDF — free, no sign-up.
- Confidential contracts: you can Password Protect PDF before sending, but never use an unfamiliar site that requires an upload.
- Dozens of files at once: your IT team can script it; for everyone else an online tool is the realistic option.
My advice
Compressing harder is not automatically better. Use the standard level for a chat preview and keep the original for printing. My routine now is: archive the original → send a compressed copy → add a password to anything important.
Try it → open Compress PDF, drop in the file that would not send, and see whether it lands inside your mail server's limit.