How to combine multiple Illustrator files into one PDF?

IT IS DEPOND ON THE VERSION.

Depending on your Acrobat version. The latest CC version allow you to combine .ai files by just clicking Combine file option in Tools tabs. Make sure all your .ai files are from latest version as well.

For older version, save as illustrator files into PDF and use combine features of acrobat.  

FOR OLD VERSION OF ILLUSTRATION i can save each AI file as PDF  then combine them using  acrobat reader pro9

- For old versions of illustrator i can save each AI file as PDF then combine them using Acrobat Reader Pro9

- For Latest version of illustrator CS5 and above i can build a Multi Art board AI file and save the final as PDF