The beauty of the PDF format is that you can open it on any platform, be it desktop or mobile. It is easy to create, send, share, read, and edit PDF documents and works everywhere. Unfortunately, some PDF files are too large. This poses problems that we will discuss below, along with a solution: compress PDF documents on Windows, macOS, Linux, Android, and iOS.

Drawbacks of Large PDF Documents

There are several issues that occur when you compress PDF documents. Some of the most common are:

  • Can’t attach large PDF files to email, as most email service providers, like Gmail, have a 25MB attachment limit.Can’t attach large PDF files to messaging apps like WhatsApp, as it has a 16MB limit.Takes longer to upload and download, especially on a slower bandwidth and under certain situations, like traveling in remote areas.Consumes more bandwidth, which can be a problem on metered connections like smartphones or carrier data plans.

Free PDF Compressor (Windows)

The first app on the list is Free PDF Compressor for Windows.

  • After installing the app, click on the “Browse” button to choose a PDF file, then select “Save as” to choose a location to save the output. By default, it will choose the same folder where the original file is located.

I have selected the ebook option to keep image quality at a medium resolution. The ebook I have selected is 9.21MB in size. You can play around with the settings to see if the final results suit your needs.

  • Click the “Compress” button to begin the process. It shouldn’t take too long to complete. The output file was just 471KB, which is pretty impressive, and took just three seconds. The text is crisp and images sharp.

PDF Compressor (Windows)

PDF Compressor is another Windows utility tool to compress PDF files.

  • Open the app and notice that the UI is a little busy. We will convert the PDF file to grayscale (black and white) to further reduce the PDF file size. Click on the Folder icon to choose a PDF file. Select the “Document in black & white – halftones” option. Choose the quality of the output file. Below, towards the bottom, you can also set the image resolution to further control the size of the output.

  • Click on the “Compress” button to begin. In our example, the 9.21MB file shrunk to 181KB.

How to Compress PDF Documents on macOS

Preview provides a native option to reduce the file size when exporting a file as a PDF; however, the results are often less than satisfactory. There are better options out there as we discuss below.

One of them is Quartz Filters. It adds additional filters to the default filters that Apple offers in Preview to reduce PDF file size. Quartz is also more consistent with the quality and size of the files compressed.

There are also several third-party apps available in the App Store.

Lightweight PDF (macOS)

  • Install and open Lightweight PDF and drag and drop the PDF file you want to compress in macOS.

  • The compression process will begin immediately. There are no buttons to press or options to select. Note that the new compressed file will overwrite the existing file, so you may want to create a copy first.

  • When the process is complete, the app will display the results.

PDF Shrink (macOS)

PDF Shrink works like Lightweight PDF but with one notable difference: when you drop the PDF file, it lets you select the quality and resolution of the output. You can play around with these values to find a balance where files are compressed with minimal quality loss.

Unlike Lightweight PDF, it will ask you to choose a download location instead of overwriting the existing file.

Ghostscript (Linux)

  • Open the Command Line tool, also known as the Terminal. If you don’t know how to do that, click on the Ubuntu icon to open Dash and type Terminal to search and open it.

  • Use the command below to install Ghostscript.

  • The command below will reduce the size of the PDF file. Note that you will need to change the name of the PDF file in the command accordingly. In my case, the file was saved in the Downloads folder. Make sure the path is correct too, as it won’t be able to detect the PDF file to compress it.

In the example above, the input file was 4MB.

And the output file was just 235KB.

Densify (Linux)

Densify is open source and hosted on GitHub

  • Open the app and be greeted with a simple GUI. Select the PDF file you want to compress and select a Type. If unsure, choose “Screen” or play around with different options until you get a satisfactory result.

  • Click the “Compress Now” button.

  • You will get a notification when the PDF file is compressed.

This quick chart explains the different compression types Densify has to offer and what they mean for your reference.

Compress PDF File (Android)

  • After installing Compress PDF File, tap on “Open PDF” to choose a file, then click on “Compress” to begin. You can choose compression level, but I found that the recommended settings were good enough. You will see a pop-up that shares how much space you saved and asks how you want to save the compressed PDF file on Android.

PDF Compressor (iOS)

PDF Compressor works like its Android counterpart.

  • Tap on the “Select PDF” button to choose the PDF document. Select one of the compression settings, then tap on “Compress PDF.”

  • You should see a pop-up with details of the compression. The compressed file can be found under the “Compressed” tab.

Drawbacks of Compressing PDF Documents

We saw why there is a need to compress PDF documents and how we can compress PDF files on various desktop and mobile operating systems. But what about the drawbacks of compressing PDF files? These include:

  • Not all tools are free. Some are paid and others adopt the freemium model.Compressing PDF files too much can reduce the quality of included images, ruining the experience for the reader.Too much compression can also break text and other elements, rendering the PDF file unreadable.

Frequently Asked Questions

1. What happens when I compress PDF files?

Images and other graphic materials in the PDF file are scaled down. That means they are recreated at a lower resolution and contain fewer pixels, hence, taking less space.

2. Should I compress PDF files offline?

There is a privacy and security risk involved when you upload files online to a third-party developer’s servers. If you think the nature of the document is sensitive, it is best to compress it offline.

3. How long does it take to compress PDF files?

That depends on the size of the PDF file. However, during the tests here, a 20MB file took less than 5 seconds to compress.

Wrapping Up

If compression is not working for you – for example, the quality is not up to par – you can break the PDF file into smaller chunks or split it. The drawback of this method is that there would be multiple PDF files, and the user would have to open each one separately.

Another option is to convert the PDF to grayscale. This is useful when the PDF file has too many images. Converting the PDF file to grayscale will turn the images black and white, along with fonts and all other color elements, reducing the PDF file size without compromising the quality.

Check out this list of options to learn how to edit PDFs on desktop and with online tools. Also learn how to combine PDF files on Windows and Linux.

A C.A. by profession and a tech enthusiast by passion, Gaurav loves tinkering with new tech and gadgets. He dropped out of CA in the final year to follow his passion. He has over seven years of experience as a writer covering consumer tech and writes how-to guides, comparisons, listicles, and explainers for B2B and B2C apps and services. He recently started working out but mostly, you will find him either gaming or streaming.

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