Adobe reader has been one of the famous pdf readers of all times . But there are also other readers available for free . Let us take Sumatra pdf for example . It opens all the pdf files in the time , in which the notepad opens a text file.It is a very good reader which takes very little system resources and it is of very little size and indeed it is a freeware .
Other pdf readers are foxit reader . The freeware version is very fast in opening pdf files however many utilities are available in the professional version.