A computer system and computer control software is provided which allows for secure document delivery between remote parties, and control by the sender of the further distribution and handling by the recipient of an electronic document or other computer file. A file in an application may be stored on a server and manipulated by the file's native application. The recipient of the file information is given preferably automatic operation to view the user output of the server application, via a thin-client system. The recipient of the file is thus limited, as dictated by the sender, as to the operations it can perform on the document via the server application. Files attached to electronic messages may also be removed and stored on a server, thus eliminating any possible effect on the recipient machine by the computer file. Also provided for is an adaptable thin-client system which adapts to local environmental and use conditions to provide the correct degree of thin-client or local application reliance.