Excel XLSX files and Word DOCX files are Zip files of XML data

Microsoft Office programs such as Word, Excel and PowerPoint create files in Open XML formats by default.   The file extensions for OpenXML format include XLSX (Excel), DOCX (Word), and PPTX (PowerPoint).

Files with names that end with “.xlsx” ,”.docx” or “.pptx” can be renamed to “.zip”.  These ZIP files can be uncompressed to reveal multiple files and folders.