Hello
Thank you for your question and reaching out. I can understand you are having query\issues related to Dark black lines across my MicroSoft document.
If you enter three or more underscores followed by the letter "Enter," you will almost surely get a paragraph border beneath the paragraph.
Use the Home Tab, Paragraph Group, Borders button, located in the group's lower right corner, to choose the paragraph that is directly above the line, then select No border.
Select the last word before that line and drag down to include the first word after that line (the selection will include the line)
Then click the Border Tool - -> Select No Border
--If the reply is helpful, please Upvote and Accept as answer--