CTRL + A – is the keyboard shortcut to Select All.
Click anywhere inside your file, e.g. Word document, PowerPoint presentation, or Excel spreadsheet.
Press Ctrl +A to select the entire document.
This shortcut works in all MS Office applications and on many webpages.
On a Mac you can use Command-A
For Example: The next time you need to quickly change the font of an entire Word document, press CTRL + A or Command + A to select the entire document, then apply the desired font.