PDF (Portable Document Format) is one of today’s most popular formats for working with electronic documents. One of the obvious advantages of this standard developed by Adobe is the ease of combining graphical information with the texts.
No less important is the fact that a PDF document opens in exactly the same style and layout on any device, which makes this format irreplaceable in the printing industry. Not surprisingly, many printing devices are capable of reading such documents directly, requiring neither the use of third-party equipment nor the installation of additional software.
Why It May Be Necessary to Reduce PDF Files
Given the variety of purposes for which the format is used, there can be a vast number of reasons for compressing files. Let’s mention just the main ones:
• saving space on the media or in cloud storage – the latter is especially relevant given that a fee may be charged for exceeding the limit;
• for the convenience of transferring the file by e-mail, via messengers, posting on social networks, blogs, and chat rooms;
• for more efficient use on slower machines.
One way or another, users have to compress pdf quite often.
The compression algorithms used today can be divided into two groups, such as those with quality loss and those without. It should be mentioned right away that the methods with loss of quality are not “bad”, for example, if you need a tiny avatar for your forum account then it is absolutely unnecessary to preserve the original quality.
Compression algorithms without loss of quality include the following:
• LZW is an adaptive conversion to TIFF and GIF formats;
• RLE is conversion without loss of quality to BMP and PCX, the resulting image is black and white, so the method is used mainly for facsimiles;
• CCITT is another dichromate imaging format used for facsimiles;
• zlib/deflate is a rather rare algorithm today.
When it comes to compression with quality compromise, the JPEG and JPEG 2000 methods are mostly used today. The most important is JBIG2, which enables users to compress color images with quality losses and black and white images without quality losses.
What Compression Method to Choose
Compression with loss of quality enables users to achieve the maximum reduction of the file weight, i.e. the space the document takes up on the hard drive or in the cloud storage. If you need to compress PDF to 100 kb, this is definitely your method. However, as the name suggests, the price of such a result is irretrievable (!) loss of data. For example, adjacent pixels of close colors blend together, the smoothness of curved lines decreases, etc. This method is definitely not suitable if the result is not final, that is, further work with the document is planned.
Compression without quality losses does not directly affect the quality of the image. It affects the additional data, such as:
• information about the author;
• page thumbnails;
• built-in print options;
• search hashtags.
The document can be used for further work but the results of such compression are rather modest.
Compression with Adobe Acrobat
Adobe Acrobat is specialized software for dealing with PDFs, so it offers the richest range of compression options. The software offers two main ways of compression – with default parameters and customizable ones.
To compress a file with default settings you need to:
• open the file in Adobe Acrobat;
• proceed to the menu, select file – save as another – PDF file is optimized;
• confirm saving.
Customizable compression is performed as follows:
• open a PDF document in Adobe Acrobat;
• proceed to the menu, select Tools – Optimize PDF – Advanced Optimization;
• select the necessary options on the optimization panels;
• confirm saving.
Important: Before saving the compressed file, be sure to change its name to avoid losing the source file.
Compression with Online Services
There are many online services for handling PDF documents, and most of them enable document compression. Taking into account that in spite of the abundance of services, all of them are designed in approximately the same way, let’s look at compression using pdf2go as an example.
First of all, select Compress PDF from the All Tools menu. Then upload the document, which can be performed in several ways:
• the file can be selected in the explorer (the explorer opens by clicking Choose File);
• drag and drop the file into a special field on the screen;
• copy and paste the URL (it enables users to edit web pages);
• “pull” a file from DropBox or Google Drive.
After that select the compression options. There are two preset options, Basic and Strong, as well as customizable compression including the following options (in order of decreasing quality):
For maximum compression, it is possible to turn the image into a black-and-white one. After that, all you have to do is click Start. Processing takes from a few seconds to a couple of minutes. The result can be downloaded or uploaded to the cloud. The latter option is available to registered users. Do not close or refresh the tab before saving the result, otherwise, the data will be lost.