PDF is short for "Portable Document Format" which was created by Adobe Systems in 1993 to facilitate document exchange. After creation of the internet this format experienced significant growth and became de-facto standard for document exchange on the internet.

Temporary files may be created by computer programs for a variety of purposes; principally when a program cannot allocate enough memory for its tasks, when the program is working on data bigger than architecture's address space, or as a primitive form of inter-process communication.

File extension BAK is given to files used for backup of another document, often created automatically by various programs or the operating system; for example, Windows may create BAK files for the System.ini and Win.ini files.

Most frequent use of RAR extension is to store compressed information archived using RAR format. It is a proprietary compression format developed by Eugene Roshal. Compressing files is very useful when you want to transfer them over the internet since compression reduces amount of information to transfer. Also you may fit much more information on your PC hard drive if you compress information that you don't use.

DAT file extension could represent following file types:

- Data file

- A data file extension used to designate an error message in a inbound internet email message (Microsoft Exchange Server v 5.0)

- WordPerfect Merge Data

- Extension used for some MPEG files

- Yahoo Messenger archive file

In computing, DLL (an abbreviation of 'Dynamic Linked Library') is a file extension for executable libraries. DLL files are commonly used by software programs to store parts of the executable code.

BIN file is short for binary file. It is impossible to open BIN files in text editor because they consist of information in binary form which could only be enterpreted by computer applications or operating system. This extension is also associated with extension used for UNIX executable files.

Direct Access Archive, or DMG, is a proprietary file format developed by PowerISO Computing for disk image files which supports features such as compression, password protection, and splitting to multiple volumes. It can be handled like a file just like other formats, such as an ISO image and BIN, but is currently only usable by PowerISO software. Popular disk image mounting programs such as Alcohol 120% and Daemon Tools currently do not support the mounting of DAA images.

APK extension is used to deliver and install application software and middleware onto Google Android system. APK file contains compiled Android application code and all resources which are required by this code.

You can open XLS file using Microsoft Excel application. Microsoft Excel is similar to other spread sheet applications that can store information that can be edited and viewed on several platforms. You can run Microsoft Excel and open XLS files on Mac and Windows through installed Microsoft Office applications.

HEIC is a new file format designed to store highly compressed photos and videos. HEIC and HEIF formats were developed by MPEG group and are currently adopted by multiple vendors including Apple and Microsoft.