Files with .doc extension, which means “Document”, are saved in format developed by Microsoft. Primarily was used for office applications, especially for text editors. As many other file formats for these applications, it is based on XML, on the same principle are created formats .odt or .docx. There are many similarities with .odt file format. For example it can handle with long and stylized texts, however it is not open file format and his using is limited only for Microsoft products. Primarily used program for creating and editing these file types is Microsoft Office Word 2013, which was also developed by Microsoft.
First versions of it were developed in early 80s, especially for program WordPerfect. Doc files were not primary, but that changed in 1990, when Microsoft released their own office suite, which already contained Microsoft Office Word. Latest version of this format was released in November, 2012. His compatibility changes through different programs. Even with apps from Microsoft its compatibility varies, because there are big differences between certain versions, sometimes files from Microsoft Word 97 are not compatible with files from Microsoft Word 2003.
Primarily used program to open these files types is Microsoft Office Word 2013, but there are some equivalents to it, which are available for free. For example there is OpenOffice.org Writer, which has one of the biggest support for this format, but he can not use all functions available in this file type. Therefore if you save file in Microsoft Office Word and you will try to open it in Openoffice.org Writer some complications might appear. Another examples are Microsoft Word Online, which is for free and when you connect it to Microsoft OneDrive service, you can use it as Microsoft Office in browser. There is also Google Docs, which can handle this format.
Browsing and editing can be achieved in Microsoft Word Online, but you need Microsoft Account to use it.