Reduce the file size of PDF documents

Gareth Saunders
Sunday 17 January 2016

A few months ago, while quality checking our new prototype website I discovered a page that was linking to three PDF files. The problem was: they were enormous.

The largest document was over 63 MB; that’s about the same as downloading 12 songs on iTunes. The smallest document, which was claiming to be for visitors using smartphones, was 2.3 MB (about half a song).

Bullet-point list showing 3 PDFs
These PDF documents are far too large.

That’s fine for a fast, university network like the one we have here, or on a fibre-optic home broadband connection; even the largest file may take only a few seconds to download.

But as the connection speed gets slower the time required to download files goes up. On my own home connection the largest file would take nearly a minute to download. On my smartphone over a basic 3G connection (typically 0.1 Mbit/s), which I have near home, it would likely take nearly an hour and a half.

Here is a table for comparison:

Uncompressed PDFs
File Size University Home Mobile 3G
Answers.pdf 61.2 MB 5 secs 50 secs 81 mins
Trail.pdf 32.2 MB 2 secs 26 secs 42 mins
Smartphone.pdf 2.33 MB <1 secs 1 secs 3 mins

Compress your PDF

The good news, though, is that often PDF files can be compressed to dramatically reduce their file size.

I usually reduce PDFs using Adobe Acrobat, because I have it as part of Adobe Creative Suite, but the software is expensive and usually beyond the budget of most users.

There are, however, free online services such as SmallPDF.

Compress PDF - reduce the size of your PDF online
Compress PDF – reduce the size of your PDF online

Simply drag and drop your PDF onto the webpage, watch the progress meter as the file is uploaded, and then download the compressed version.

Success varies from PDF to PDF depending on what the file contains but it can be very worthwhile, and even a 10 KB reduction still means that your file is saving somebody’s bandwidth.

File Uncompressed Compressed
Answers.pdf 61,200 KB 249 KB
Trail.pdf 32,200 KB 135 KB
Smartphone.pdf 2,330 KB 263 KB

The impact this has on download times is notable, especially for users of smartphones.

Compressed PDFs
File Size University Home Mobile 3G
Answers 249 KB <1 sec <1 sec 19 secs
Trail 135 KB <1 sec <1 sec 10 secs
Smartphone 263 KB <1 sec <1 sec 21 secs

Of course, whether this file should actually be a PDF or converted into a webpage is a whole different ballpark of worms. A topic for another day, perhaps.


If you have to upload PDF files to the University website (or even simply send it via email) then I urge you to consider people’s bandwidth and reduce your PDF.

Incidentally, if you are creating a document to upload to the University website in PDF format, I also urge you to download and use the University branded Word template which may be downloaded from the corporate identity page (password-protected for staff only).

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One reply to "Reduce the file size of PDF documents"

  • Paul Clerkin
    Paul Clerkin
    Thursday 18 January 2018, 12.38pm

    Hello Gareth! Love the article, though I would because I'm in the business of making PDF compression websites :) I notice that you're listing SmallPDF as the option for compressing files online. As the builder of a compression tool (WeCompress) I thought I'd chip in because SmallPDf is no longer totally free (if you want to do multiple files), and our tool is! WeCompress also reduces whole host of other file types, so there even more scope for saving the bandwidth of folks using the University website! Cheers, Paul


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