There is many times necessity of upload/download data between use’s frontend and SAP’s application server. If it is a high volume of files usually we use FTP tool. However from end user perspective if it is a case of few files there are other ways of how to do it.
We can create simple ABAP programs for the users. In such a program a Function Modules like GUI_DOWNLOAD and GUI_UPLOAD.
Also we can reuse ABAP classes like CL_GUI_FRONTEND_SERVICES with its methods: GUI_DOWNLOAD and GUI_UPLOAD.
However much easier method is to use standard transaction codes:
CG3Y - copying from app server to frontend
CG3Z - copying from frontend to app server