Reducing PDF size: how to do it

Ideally, you should try to keep a PDF document as small as possible even in the initial process of creating it. Here, a simple rule applies: less in­for­ma­tion means a smaller file size. Pictures es­pe­cial­ly should be com­pressed in advance. This is best done through picture editing programs like Photoshop or Gimp.

Besides the mea­sure­ments and color depth, the most important factor when doing this is the image res­o­lu­tion, which is indicated in units called “dpi,” or “dots per inch.” Halving the res­o­lu­tion from 600 dpi to 300 dpi no­tice­ably reduces the size of a PDF, from ap­prox­i­mate­ly 4.55 megabytes to 2.68 megabytes. When choosing a res­o­lu­tion, you should always consider the purpose for which the PDF file is being created. If it only needs to be read on a computer screen, 72 to 96 dpi are suf­fi­cient. On the other hand, for a printing template or pre­sen­ta­tion, you shouldn’t go lower than 150 dpi, and 300 dpi would be optimal.

If you have an already-completed PDF in front of you, or you aren’t the creator of the file, you usually can’t avoid a belated com­pres­sion if you prefer a smaller file size. However, this is commonly the most in­con­ve­nient method, because a belated reduction of the res­o­lu­tion is always made at the expense of image quality – even if the loss of image data is curtailed enough that a clear result is achieved. There are various tools for belated com­pres­sion, which will be briefly in­tro­duced and explained in the following section.

Of course, you can compress a PDF with the help of WinZip quite easily. The dis­ad­van­tage of this, though, is that you have to unzip the file to open it. Meanwhile, other tools allow you to reduce PDF size directly. This can only happen on the condition that the document in question is not protected with editing re­stric­tions. In this case, you first have to remove its “read only” status.

Adobe, the company that orig­i­nal­ly created the PDF file format, also provides a tool for com­press­ing such files: the fee-based Acrobat Pro DC (not to be confused with the free Acrobat Reader). After you have opened the document in question in this program, you can click “File” > “Save as Other” to create an “Optimized PDF”. In the window that opens next, you can use the button at the top right to review how much storage space in­di­vid­ual elements (fonts, images, bookmarks, forms, and comments, for example) take up.

Apart from these firmware tools, there are countless other programs that you can find as freeware on the internet. They are generally free, can be quickly installed, and are easy to use. PDF24 creator is a popular and practical example for exactly these reasons.

Upon in­stal­la­tion, PDF24 functions like a driver for a virtual printer. After opening a PDF with a reader or a different program, you click “Print.” You then choose PDF24 from the list of available printers and confirm the entry. Instead of the PDF document being printed at this point, the PDF24 launcher is opened. A single click on “Compress PDF Files” transfers you to the PDF24 compress tool. Here, you can adjust various com­pres­sion pa­ra­me­ters and choose a storage location for the PDF file you will create.

Al­ter­na­tive­ly, the PDF24 creator can be used as an in­de­pen­dent program. You can use it to search your computer for the file that is to be com­pressed, or simply drag-and-drop the file into its interface. Like many other kinds of software, the PDF24 creator offers several in­ter­est­ing ad­di­tion­al functions, including a PDF viewer, different en­cryp­tion methods, and the pos­si­bil­i­ty to combine multiple PDFs into a single document or to remove in­di­vid­ual pages. 

Examples of other freeware tools are the BullZip PDF Printer as well as doPDF, which are also installed as printer drivers. Except for minor dif­fer­ences, these function exactly the same as PDF24. Which tool you decide to use depends on personal pref­er­ence. However, caution is advised with lesser known, free programs or those offered by un­trust­wor­thy third-party providers: these in­stal­la­tion setups can include countless ads and unwanted ad­di­tion­al com­po­nents.

When you want to quickly reduce PDF file size, online tools can present an al­ter­na­tive. These are available as web apps in a web browser. Using the file search or drag-and-drop functions in these apps, you can usually upload one or even several PDFs. The com­pres­sion then takes place in the cloud of the website operator – there is no need to install a program or make use of your own computing capacity.

The Internet is home to countless free service providers, notable examples of which are SmallPDF, PDF­Com­pres­sor, and PDF2GO. Just as with the many freeware programs, their sim­i­lar­i­ties when it comes to use and functions are very pro­nounced. The numerous ad­ver­tis­ing banners make these websites somewhat confusing at first glance, but the ads merely serve to finance this free service.