In case anyone else is interested to know, I was able to obtain the total number of attachment downloads grouped by files using ODBC logging and a little SQL. Here is what I did:
1. Configured ODBC logging for the IIS site on my 2008 R2 Server. You need to use the 32-bit SQL driver since this app is 32-bit and not 64-bit.
2. With all my logging data now in a table called 'InternetLog' I am able to run the following which will show me a list of all the PDF and DOCX files that have one or more downloads sorted descending by total number of downloads for each file:
Essentially I select all the text to the right of the equals sign from the target field for the file name. Then I just count up the occurrences. I still think that this type of information should be handled in the product as IIS ODBC logging can be a substantial overhead, but this works for me.
select SUBSTRING(target, CASE WHEN CHARINDEX('=', target) > 0 THEN CHARINDEX('=', target)+1 ELSE LEN(target) END, LEN(target)) as 'filename', COUNT (*) as 'total' from InternetLog where target like '%.pdf%' or target like '%.docx%' group by target order by total desc