The Top Pages report has a column `Visitors` which is always defined as the unique number of `human` visitors to the page within the given date range.
The Top Pages Details report shows the `Unique IDs` column, this includes humans and bots, crawlers, scripts etc. But most importantly, the Details report groups the results by page including query parameters and that can create a huge difference with the Top Pages report, which only goups by page and does not look at parameters.
To answer your question on which is more accurate, if you are interested in the number of real people that downloaded your pdf, the Top Pages repört is more accurate.
If you are interested in how many times your pdf file was downloaded from any requester, including bots, in each parameter variation, the Top Pages Details report would be more accurate.
I hope this helps!