File extensions

Microsoft's help file format — HTML plus assets compressed with LZX. Widely used for online help in Windows software since 1998. Still actively distributed in China, Japan, and Korea.

The pre-2007 binary Word format (Compound File Binary). Still circulates in government and SMB workflows and carries a high malware-delivery risk because of embedded macros.

The default Word document format since Word 2007. Under the hood it is a ZIP package of XML and media — portable enough that most apps can open it.

The IDPF / W3C standard for e-books. Under the hood it is XHTML + CSS + metadata inside a ZIP — designed for reflowable text.

The native format for Apple's Keynote presentation app. Known for smoother transitions and cleaner typography than PowerPoint.

The early Amazon Kindle e-book format. Amazon has since moved on to AZW3 and KFX; MOBI is legacy.

The native format for Apple's Numbers spreadsheet. Each sheet is a freeform canvas hosting multiple tables and charts.

The ISO OpenDocument presentation format. Native to LibreOffice Impress and convertible to/from pptx.

The ISO OpenDocument spreadsheet format. Native to LibreOffice Calc and broadly interoperable with xlsx.

The ISO-standardised open document format. Native to LibreOffice and OpenOffice, and broadly interoperable with docx.

A document created by Apple's Pages word processor on macOS / iOS. Internally a ZIP bundle of XML and preview imagery.

A fixed-layout document format used anywhere the exact look of a page matters — contracts, invoices, manuals, and printable forms. PDFs render the same way across OSes and printers.

PowerPoint's pre-2007 binary format. Still shared in government and large enterprises; macro-enabled variants need the usual caution.

PowerPoint's format from 2007 onward. A ZIP bundle of XML and media that also opens cleanly in Keynote and LibreOffice Impress.

Microsoft's cross-platform formatted-text format. Richer than plain text, and the lowest common denominator for formatted documents on every OS.

The pre-2007 binary Excel format. Still emitted by legacy enterprise systems and a classic malware delivery vector because of VBA macros.

Excel's default format since 2007. Under the hood, a ZIP bundle of XML and media — also readable by Numbers and LibreOffice Calc.