nope dont need to zoom in lowering the margin makes it so the space on the border of the page is smaller, as you can see from your pics the alignment marks are inside the page fairly far, if you lower the margin to like 5 or 6 those marks will go all the way to the page end (if you do borderless print) doing that increases the area of wich you can fit parts per page, more parts per page = less paper used up
if your not worried about paper you dont need to worry about margins.
ideally you want the alignment marks as close to the edge of the paper as you can if you ever print any parts that go beyond the paper so you can align the paper up and tape together before you cut out the part.
as for converting to PDF as long as your friend saved it for what ever paper your useing IE Letter/A4 before converting to PDF you shouldnt have a problem when you print it from adobe