Every shortcut below works on Word for Windows. On a Mac, swap Ctrl for Cmd in almost every case — the few exceptions are noted.

General
ShortcutWhat it does
Ctrl + NNew document
Ctrl + OOpen
Ctrl + SSave
F12Save As
Ctrl + PPrint
Ctrl + WClose document
Ctrl + ZUndo
F4Repeat the last action
Editing & formatting
ShortcutWhat it does
Ctrl + B / I / UBold / Italic / Underline
Ctrl + Shift + CCopy formatting (Format Painter)
Ctrl + Shift + VApply copied formatting (Format Painter)
Ctrl + SpaceClear manual character formatting
Ctrl + Alt + VPaste Special — choose “Unformatted Text” to strip formatting
Ctrl + L / E / R / JAlign left / center / right / justify
Navigation
ShortcutWhat it does
Ctrl + Home / EndJump to the start / end of the document
Ctrl + FOpen Find and the Navigation Pane
Ctrl + GGo To a specific page
Ctrl + ← / →Jump one word at a time
Working with text
ShortcutWhat it does
Ctrl + Shift + >Increase font size
Ctrl + Shift + <Decrease font size
Ctrl + KInsert a hyperlink
Ctrl + EnterInsert a page break
Ctrl + BackspaceDelete the previous word
Review
ShortcutWhat it does
Ctrl + Shift + EToggle Track Changes on or off
Ctrl + Alt + MInsert a new comment

A note on paste-without-formatting: many apps use Ctrl+Shift+V for this, but Word has historically been the exception — that combination is Format Painter here instead. Microsoft has been rolling out a true plain-text paste shortcut in newer versions, but Ctrl+Alt+V → Unformatted Text remains the version that works everywhere.