One paragraph arrives from a website with an oversized font and a coloured background. Fixing each line by hand is possible, but first check whether the paste operation brought in formatting you never wanted.
Word offers different paste choices. Keep Source Formatting retains the original appearance; Merge Formatting adopts much of the destination style; Keep Text Only removes source formatting and nontext elements. Available choices depend on the content and Word version.
Try a small passage first
In a spare document, copy a short paragraph containing one heading, an emphasised word and a link. Paste it, open the paste options and compare the result with what you need. Use the actual Word version in which you will finish the document; do not assume every web, mobile and desktop interface is identical.
If you only need the wording, text-only pasting is a useful starting point. If emphasis carries meaning, check whether it survived the chosen option. A table needs special care: text without its row-and-column layout can become difficult to interpret.
Rebuild the structure deliberately
Apply your document’s heading and list styles where appropriate. Check paragraph breaks, list numbering and link destinations. A heading that merely looks larger may not behave like a heading in navigation or the table of contents.
For repeated work, consider a default paste preference only after the sample behaves as intended. Keep the original source available until the result is checked. A tidy font does not establish that the wording, quantities or links were copied correctly.