I am sure you probably already are there... but there are two ways I look for things ...
First, use the "Search" for function on the computer ... start button or some such. I would limit such a search in this case to "*.pdf files" and "last one day" and possibly even "size greater than 500kBytes" (but that would be overkill)
Second method, ask for the download again, and note where the application is actually saying that it will be put (usually works) and halt the download of most of the file...
/
actually, where many applications choose to put a file depends on the "extension" ( .pdf ) so you don't actually have to reload the same file to find out where it got put. any similar file will go the same place unless you explicitly change it.