Since many years now Adobe as the driving force keep on publishing their pdf format as a "de facto standard" mainly established for online and graphical documents. Due to the fact that a document standard should be usable for all users (for reading) Adobe published the free Adobe Reader for PDF documents.
For all these things, there are a number of Adobe products - paid products in a high cost range. Since version 1.0 of the PDF specifications many years have passed and with each new version of an Adobe Reader installation the required harddisk space increased by many megabytes. This fact called the Open source community into action. Source Based on a free library like e.g. Ghostscript alternative ways of free PDF creation as printer drivers were developed. These printer drivers are usable inside most office products. Two well known free pdf printer drivers are PDFCreator and FreePDF. In the meantime there are some more free pdf readers published. There are portable versions, too. So there's no need to install - only copying anywhere onto the harddisk. That's all.
One of the best adobe alternatives - perhaps the best - regarding free pdf readers is the well known Foxit PDF reader. While an Adobe Reader 10 installation needs about 457 mb harddisk space, the Foxit Reader 5.4.2 comes along with slim 44 MB! ... And less megabytes means less harddisk space and this means often higher processing speed and a faster start, too! An additional hint: If you only want to read/show pdf documents the small "Sumatra PDF" (specially the portable version) is all you need.
What could be the reason for a big company like Adobe spending a lot of money to establish a document standard? ... Of course 'cause they are always the first with new pdf-products to earn money ;-) So actually there's not only the Adobe Reader but also the high-priced products from the Adobe Acrobat series that allow everything related to the creation of PDF documents.
That pdf-products can be much cheaper (with a comparable quality) is proving the Foxit Corporation - Manufacturer of the free Foxit PDF Reader. Started with the free Foxit pdf reader, now the company offers a wide range of lean and more cost-effective products for the development and editing of pdf documents. The products are running on nearly any technical basis (windows, iOS, Android, ...). This ranges from applications for PDF editing and creation up to complete developer sdks. All this with a very "nice price" licensing procedure.
As a developer in the pdf environment of course i have several products and versions of pdf readers and various versions of the Adobe Reader installed. This allows me for example to say "runs on Adobe ... too". But in my daily business i'm just using the Foxit Reader - Give it a try ;-)