Convert LIDAR data

We have an ASCII file containing LIDAR points. The file is about 1GB in size. I want to use LIDAR tools in Power Civil to filter and process the data into a TIN for drainage analysis. The problem I have is there are 2 additional fields in this file besides xyz which are preventing me from reading the file with the LIDAR tools. Are there any other tools available that I can use to manipulate or process this data? Perhaps a custom parsing filter?