For example, you have some text in Times New Roman 12pt, and you copy it into another document. When you copy text, the format of the text can change. If you haven't done anything to change it, The default out-of-the-box style is Normal style. All text has an underlying style, even if you've never applied a style to any text.
The formatting of all text in your Microsoft Word document depends on styles. Sometimes you copy text from one document to another, and the format of the text changes. When text is copied from one document to another, it retains direct formatting, but otherwise takes on the formatting of the style in the receiving document. Word thinks you're copying text in, say, Body Text style. You think you're copying Arial 10pt text. Format of text copied from another document