I have received and SDL Trados package, why can't I add files to the project?

SDL Trados packages are self contained with TM, glossaries and reference files in some cases. Adding files to a Smartcat project created around one of these packages would impact the integrity of the structure. In addition, any file added would not be part of the return package created by Smartcat once the project is completed. Therefore it is not possible to add either a new file for translation or reference files to these projects.