HydroCAD automatically saves every project using the earliest file format possible. For example, if a project uses only features that were available in HydroCAD-6, it will automatically be saved in HydroCAD-6 format, even if the user is running HydroCAD-7 or HydroCAD-8.
However, as new features are added in each version, they may require new file "vocabulary" that is not understood by earlier programs. For example, if a prefab storage chamber is used with HydroCAD-7, HydroCAD-6 will not be able to open the file, since it doesn't understand the chamber specifications in the file.
If you attempt to open a file that contains newer features, HydroCAD will report the first line that it doesn't understand. The best way to open the file is to obtain the latest HydroCAD update. In some case, you may also be able to ask the project's author to remove the newer features and re-send the file. However, this is feasible only if the features aren't essential to that specific project. In most cases the project requires the newer features, and you will need to get the latest update in order to open the file.
For further information please read about HydroCAD file compatibility at www.hydrocad.net/filecompatibility.htm
