Final answer:
To change the entire left margin of a document, the feature to use is Page Setup, not Page Break, Paragraph Alignment, or Tab Settings.
Step-by-step explanation:
The feature that allows you to change the entire left margin of a document is known as Page Setup. When you want to adjust the margins in a document, especially in Microsoft Word, you would navigate to the Page Layout or Layout tab depending on your version of Word, and then click on the Page Setup dialog box launcher. Here, you can set the exact measurements for your document's margins. It is different from a Page Break, which is used to start a new page; Paragraph Alignment, which adjusts how your text is displayed within the margins; and Tab Settings, which control the position of the tab stops within a line.