The default file formats for Microsoft Word documents depend on the version of Word you are using :
.docx → Default format for Microsoft Word documents (XML-based, smaller file size, better compatibility)..doc → Default format before Word 2007 (binary format, larger file size)..dotx → Word Template (used for reusable document templates)..docm → Word Macro-Enabled Document (for documents with macros)..rtf → Rich Text Format (compatible with multiple word processors)..txt → Plain Text (no formatting)..pdf → Portable Document Format (read-only format).