.pdf and AcroExch.Document
File extension RAR stands for Roshal Archiver. In the same way PK in PKZip stands for Phil Katz. Storing information in a way we see it (words, paragraphs, pages) is very space inefficient. That is why computer scientists invented lots of multiple ways to compress the information. It is actually quite simple to understand who basic principle of compression works. For example if you have document which consists mostly of words "dog" and "cat" you can replace "dog" with "*" and "cat" with "+". Thus "dog chases cat" would look like "* chases +".
.3gp and QuickTime.3gp
File extension DAT stands for DATA. This file extension is used by huge number of applications to store different helpful textual and binary information. Files with DAT extension usually tends to be quite huge.
.torrent and Opera.HTML
If you have problems with any of the format above try finding an application which corresponds to your format.
.pps and PowerPoint.SlideShow.8
Also I'd like to cover one bonus file extension since it became very popular in the age of internet. It is file extension XPI. This extension is used by Mozilla Firefox for installing Firefox extensions over the internet.
.dll and dllfile
File extension BIN stands for BINARY. Binary is a way of representing information in a way which computer could more easily understand. You probably heard that computer doesn't count in a way we do from 1 to 10 but does it in a different way using binary systems where there only 2 digits - 0 and 1. So number 2 will be codes as 10, 7 as 111. So BIN files are usually used to store information coded in binary form which application could use during its work.
.mp4 and Microsoft.Zune.2.MP4
M4A file extension is just a variation of MP4 file extension used by Apple Corporation to deliver multimedia content. This file extension became popular due to wide sread of Apple IPods and ITunes.
.bin and UltraEdit.bin
File Extension FLV is used to store Macromedia Flash Player files. After Macromedia was purchased by Adobe it was renamed to Adobe Macromedia Player. This is the most popular format for multimedia information on the internet. It can transfer vector graphics, stream video, audio and text. One big advantage of it is that it has a programming language embedded in it and sotware developers could code very advanced internet applications using it.
.dat and data-file
MP4 file extension stands for MPEG-4. It is essentially identical to MOV format and only differs by providing some additional metadata. MPEG is a set of compressions methods for audio and visual data. MP4 file extension is supported by multiple applications including Apple ITunes, XBox 360 (support added in 2007), QuickTime and other multimedia players.
.rar and WinRAR
One more possibility is that you have a windows registry error. To check for registry errors you could download registry cleaner.
.unknown and Unknown
File extension MOV was created for Adobe Quicktime application. Files with extension MOV are used to store video and music information. Advantage of this format is that it allows to store information compressed by different algorithms. Though it immediately creates a disadvantage. You need to have a specific codec installed on your computer to play some of the MOV files.
You can fool some of the people all of the time, and all of the people some of the time, but you cannot fool all of the people all the time. - Lincoln -
Experience is the name everyone gives to their mistakes. - Oscar Wilde -
Always borrow money from a pessimist; he doesn't expect to be paid back. - Unknown -
Few are those who see with their own eyes and feel with their own hearts. - Albert Einstein
Never learn to do anything; if you don't learn, you'll always find someone else to do it for you. - Mark Twain -