When might you use 'Ctrl + A' in a document?

Using 'Ctrl + A' in a document is primarily for selecting all content within that document. This keyboard shortcut is particularly useful when you want to apply formatting changes or copy everything in the document without needing to manually drag your cursor over the content. By selecting all text and objects, you can quickly execute other commands, such as copying or formatting to ensure a uniform appearance across all elements. This functionality enhances efficiency, especially in longer documents where manually selecting content could be time-consuming.

The other choices focus on different tasks within document handling. Pasting copied text, undoing actions, and spell-checking are performed through distinct keyboard shortcuts, each designed for specific functionalities that do not involve the same broad selection as 'Ctrl + A'. Understanding the unique purpose of each shortcut helps improve overall productivity when working with documents.