How to choose the right PDF compressor for your job
Large PDF files are harder to share and slower to open, so individual users and organizations are always looking for ways to reduce PDF file size. Currently there are a great number of tools to compress your PDF files both online and offline. Generally there is very little difference between each service - they all compress file sizes by approximately the same amount and the compressed files are usually indistinguishable from the originals when compared side-by-side. Some compress slightly more than others but occasionally have a lower quality output, and some have additional features to help you with the task in hand. There are also a bunch of restrictions on many of the sites which can be frustrating when trying to complete a task.
How do I choose the right service for my specific PDF-related task?
Good question and one that’s not easy to answer until you have spent many hours testing each service. To save you the time, I have analyzed the free offerings of the top 15 ‘PDF file compressors’ that appear in Google’s US search results.
Here are our reviews and top picks for tools to tackle 5 of the most common PDF compression tasks.
Uploading 5-10 files for same-time compression
Our pick: 
PDF Compressor
Control PDF compression levels
Customise the compression settings for more or less reduction.
Our pick: 
PDF Converter
Compress large PDF files online
Compression of large PDFs over 50MB in size
Our pick: 
CloudConvert
Compress PDF and other file formats
Compress other image and document formats
Our pick: 
WeCompress
Frequent or regular PDF compression
For those who need to compress more than a few files a day.
Our pick: 
NXPowerLite Desktop
Compress batches of PDF files
Of the many services, I found just a few that, without gated restrictions, allowed me to upload batches of 5 or 10 files for compression; PDF Compressor, I Love PDF, CloudConvert, and PDF24 tools.
PDF Compressor handled the compression of multiple files really well and I was unable to find a limit on how many files that can be processed. Its processing of files is performed sequentially, so as one file finishes and becomes available for download, the compression of the next file starts.
The thumbnail of each file and the history of all files uploaded in the session is really useful, as well as the ability to download individually or as a batch of files. The only slight drawback was that the interface only fits a maximum of 5 files in view at once. So when I added 10 files I found it a little difficult to manage them.
CloudConvert has a different approach to showing multiple compressed files because it vertically stacks them for download, so it is easier to see 10 or so compressed files. Somehow though it didn’t flow as well as when using PDF Compressor.
I still prefer to use an offline PDF compressor software (see below), however, if you cannot use offline software, I would thoroughly recommend the easy experience offered by PDF Compressor.
Control PDF compression levels
Why do you need different compression levels for your PDF files? Well you could be trying to get the file down to the smallest possible size or you have some PDFs that are going to be used on high-definition screens so they need to retain most of their image quality and still look sharp. Ultimately there is a tradeoff between size and quality but it can be useful to decide your preferred output.
PDF24 Tools provides straight-forward simple options for changing DPI and JPEG quality. Once the file was uploaded, it allowed the user to try multiple variations of each and get the size vs quality ratio exactly as they want.
The drawback to their approach is it is hard for the average user to understand what DPI and quality adjustments may do to their file. So it could take a lot of attempts before you achieve an optimally compressed file.
For a more guided approach to variable compression settings CloudConvert has great preset profile options depending on the intended use of your compressed file.
There are easy upfront options that are optimized to get the smallest files for web, print, archive, mrc (scanned documents) and max compression.
However, my recommended service for compression options is PDF Converter. Not only does it have preset profiles for ‘Good compression’ and ‘Extreme compression’ it also allows you to set a plethora of custom compression options.
You can select different compression settings for the three categories of image types as well as being able to selectively remove optional content items and subset fonts. It does boast full control of the compression, however, you will likely hit the 2-file daily limit pretty quickly.
Compress large PDF files online
All of the services I tried allow uploading PDFs up to 50MB which probably fits most use-cases for file compression. If you have files that are in the GBs range (I tested using a 1.2GB PDF) then there are very limited options and only two that allow compression of any large files without having to sign up for a premium account.
PDF Converter is a good option too for large files with its variable compression options, clean interface and a very clear progress bar. However, as mentioned above the 2-file a day limit seemed an overly harsh restriction.
My recommendation for large PDFs is CloudConvert. It has a super-slick interface and handles the uploading and processing of large PDF files with ease. It doesn’t restrict the number of files you can upload in any one 24 hour period but it does restrict you to 10 conversion minutes. I assume this is the time the service spent processing your file (not uploading or downloading) so it makes it hard to predict how many files you can process.
As good as the two options are in this category my advice would be to not use an online service. Large files take a long time to upload and download and you can run into issues if the connection drops en route. Add to that the restrictions placed on the services and you will get a really slow and frustrating experience. Offline compression software is definitely the better option for very large PDF files.
Compress PDF and other file formats
It’s probably a good bet that if you need to compress PDF files online you also have files in other formats that would benefit from a reduction in file size. For example, website designers have lots of images and other documents that need to be as small as possible to increase the speed of their sites.
Most online PDF compressors have other useful associated services, like merging and splitting PDFs but only two offered compression of other file types.
As well as PDF files, CloudConvert allows you to compress image formats JPEG and PNG. My recommendation though is WeCompress, which can also compress TIFF images plus the main Microsoft Office formats, PowerPoint, Word and Excel.
Supported formats can be dragged onto the WeCompress main screen and the levels of reduction that can be achieved for each file format are similar to that of PDF compression. Just like with PDF files, each file remains the same after compression - so they are easy to share with others and there’s no need to unzip them.
Frequent or regular PDF compression
Online PDF compressors are great for infrequent compression or when you are up against a tight deadline. However, if you have a regular need to compress PDF files or run into any of the issues highlighted above you probably want to consider an offline PDF compressor. As well as the same great compression it will give you fast, secure and more reliable file reduction with flexibility on compression settings and batch processing. So for regular file compressors the experience should dramatically enhance their productivity.
A number of services have offline compressor software associated with their service. Most require a premium account to access the software and they will also perform a myriad of other functions. If however, you wish to just compress files then you should look at NXPowerLite Desktop.
It is free to try for 14 days and thereafter $48 for a perpetual license, and is available for Windows and Mac. Just like its sister online service WeCompress, it produces great compression results with the supported file formats: PDF, PowerPoint, Word, Excel, JPEG, PNG and TIFF. The Windows version allows you to easily add folders of files and also has automatic compression of email attachments if you are using Outlook or Lotus Notes email clients.
There are no file size limits and batches of files are limited to 10,000 in one go! It is super-easy to use and is designed to fit perfectly with numerous workflows for improved productivity.