Basically, you build up a command line that tells the program to scan the document and put the result in a pdf file that you've named according to some rule so that the files can be found and identified later. Then you invoke a shell command so that the computer will execute the command line.
In order to view the file from inside Access, you need to invoke another command line that tells it which file to open up and which program to open it with.
We were looking to scan the material certificates for all of the metal parts we received and to print them all back out when the government asked to see them. The biggest problem was storing the files - we estimated that one year's worth of files would take 500 GB of space and we needed to have them available indefinitely.