When you copy/paste content from an external source such as a Word document, or content received by email, use the appropriate functionalities in your publishing tool. This will be a good starting point for the following recommendations.
Use the function “Paste from Word” for copy/pasting content from a Word document, so that you can keep the bold type, formatting of lists, etc.
Use the function “Paste as plain text” to copy/paste from all other sources (email, web page, etc.).