Document files are usually a text file that is created to store a document primarily on a computer.  They are used for a few other instances such as in binary files but for most uses it is a form of text file.  Currently most would agree that the standard is File Extension DOC ^[1] as these are the files that come from the popular Microsoft Word program.  Many programs are able to open these files but since *.doc is a licensed property of Microsoft it is a proprietary format so it is not opened by all word processors.  The two original formats in the window field have *.txt that is a plain text document which is used with Notepad in Windows.  Secondly is *.rtf that has been used in Microsoft Works and other document programs.  RTF is generally viewed as a format that can be exported reliably to another format.

One of the bigger players on the document creation field as been WordPerfect who’s files are saved in a few different types over the years including *.wpd, *.wp, *.wp7.  WordPerfect was once the leader in the market but has been fading in recent years.  With new technologies there are a variety of formats that are coming into the fore front.

Adobe has made famous the File Extension PDF ^[2] with its Adobe Acrobat software.  This is an open source format which has a variety of different readers out on the market with the most common a free version of Adobe Reader.

With the prevalence of the internet and portable devices occurring there a increasing chatters for a standard in document types.  Most companies have agreed that XML will be the format for future documents.  These include the extensions *.docx, *.odt, *.sxw are all a form of XML and can be opened by most new document programs.  For the portable world there is PalmDoc which can easily be read in PDA devices.  There are freeware programs that are out on the internet to convert documents into to PalmDoc for portable viewing.

There are also documents which allow viewing structured content like spreadsheets and presentation. The best for spreadsheets is File Extension XLS ^[3] which is supported by Microsoft Excel. There are multiple applications available for presentations too. But the best so far is Microsoft PowerPoint which works with File Extension PPS ^[4].

For viewing files over the internet HTML has been the standard.  This is an open source format that all internet browsers can read and will present the Web Site with a variety of different options from the creator including text and images.   As the internet has evolved there have been a couple of additions but HTML is still considered the standard.

There are other formats out there such has *.HLP for help files and *.DJVU that is just a highly compressed PDF file.  For almost any format there are convertors to place these in the format of your own choice.