A filename extension is an identifier specified as a suffix to the name by syntax, often separated from the base filename (by, e.g., a dot, a space), that indicates, e.g., the encoding (file format), the usage, of a computer file. Examples of filename extensions are .png , .jpeg , .exe , .dmg , and .txt .
.doc
doc, DOC
For most typical Word documents the extension is .docFor Excel workbooks (spreadsheets) the extension is .xlsIn general the file extension is the 3 letter/number "code" after the period in the complete file name that gives a hint as to what type of file it is. For example, in the file name resume.docthe word resume is the file's actual name and the .doc tells you that it is a document file.
extension to obey
The extension. It tells Windows what kind of a file it is. For example, a file with the ".doc" extension is a Microsoft Word Document.
.docx
* The file extension of a Word document is .doc * The file extension of an Excel speadsheet is .xls
A file name extension "associates" that file to the program or type of program that created it. For examples:.bmp = Paint.jpg = Photoshop or other graphics program.txt = Notepad.doc = MS Word 2003,docx = MS Word newer versions
.docx The extension docx is used in Word 2007.
A Microsoft Word file has a .doc extension.
.htm
"Docx" is the default file extension for Word 2013 edition.