Achieve / Zip / Compression Programs
When it comes to achieves the name winzip automatically comes to mind, but its small in size, its free and it gets the job done, this freeware program will open most of the achieves you will come across.
7-Zip (Archieve) - http://www.7-zip.org/
Adobe Acrobat Reader
Acrobat reader is widely and most used program when it comes to pdf, but as far as we are concerned it is heavy on resources and honestly does install many unnecessary features (crap or blotware) which one might not want. If you are the sort of person who wants a simple to use and low on machine resources pdf reader than I will strongly suggest foxit reader to you.
Foxit Reader (PDF Reader) - http://www.foxitsoftware.com/pdf/rd_intro.php
May sound strange why we want to include an alternative to a program which is already included for free in Windows, well·Although Windows Notepad does gets the job done but lets admit it, its undermined and that is because it lack features which could make it a powerful WYSIWYG editor, this was deliberate on part of Microsoft team in our opinion to differentiate notepad from its elder brother Wordpad.
Following are few screen shots directly from developer's website to give you a better idea of its features
Multi Document And Multi-View
XML Syntax highlighting and folding
HTML (and embedded php, java script) Syntax highlighting and folding