When you combine PDF files in Acrobat to a single file, the file order is alphabetical by default. So if you want to merge these files:
1.pdf
2.pdf
(...)
9.pdf
10.pdf
11.pdf

Acrobat will sort them like this:
1.pdf
10.pdf
11.pdf
2.pdf
9.pdf
(...)

This is obviously wrong, and the only way to fix it is to re-order them manually, which is tedious at best and can be a real problem if you have hundreds of files.

That's why I created this tool to merge PDF files according to their true numeric order. My tool will add the files in this order:
1.pdf
2.pdf
(...)
9.pdf
10.pdf
11.pdf
And if there are any files with non-numeric names (like index.pdf), you can choose whether to append them at the beginning or the end of the file.

Here's how the application looks:

NOTE: This application does NOT require you to have Acrobat or even Reader, and it will run on both Windows and Macintosh computers.
You do need to have Java installed, though.