When you use the top auto-document feeder to scan or copy a page and it results in lines across the scan/copy, there is something on the strip of glass indicated below.
The fix? Clean the glass well. 100% of the time, this is how you fix this issue.
If that doesn't fix the lines, you have not cleaned it well enough. If you put a paper with the line(s) face down in the top left corner of the big pane of glass, the line(s) will line up with exactly where you need to clean the glass strip.
Clean it. (Here's a video if you would like one.)