PDF files are not safe if you are using Adobe Reader or Adobe Acrobat to open them. Malicious PDF files are the most common vector of infection on the Web and, increasingly, in email. These malicious PDF files exploit vulnerabilities in Adobe Reader and Adobe Acrobat. Exploits of vulnerabilities in Adobe Reader / Acrobat were the most common cause of drive-by malware infections in 2009 and remains the highest in 2010.
To lower your own risk of infection, uninstall Adobe Reader / Acrobat and use one of the free alternative PDF readers listed below.
1. Mac OS X Preview
If you're a Mac OS X user, the built-in Preview feature can be used to read PDF files. OS X even includes functionality that lets you insert/remove pages from a PDF and do some other limited editing. Mac OS X Preview is the best / safest option so start with Preview and only a dedicated PDF reader if you need additional functionality.
2. CoolPDF Software
CoolPDF Software is a lightweight self-contained free PDF reader that supports both 32-bit and 64-bit versions of Microsoft Windows 7, Windows Vista, Windows XP, Windows 2000, and Windows Server 2008/2003/2000. CoolPDF Software lets you view, print, and convert PDF files to TXT, BMP, JPG, GIF, PNG, WMF, EMF, and EPS formats.