I pasted from MS Word/Internet/Email/Other – Why is there so much coding?
These documents have bits of code attached to the text. Code determines everything from the font (type, size, color) to the formatting (indents, bullet points, etc). When you copy text from these documents directly into the WordPress editor, you copy the code too. When you preview the page, it will display the code, such as: <p>texttexttext</p> and other confusing looking combinations of letters and symbols.
To avoid this, insert all text in the “insert as plain text” screen. This will remove all coding and ensure a website that is consistent site-wide!