If the file is fixed length, every record will be the same length -- if shorter, it will generally be padded to the record length with spaces to the right. Whether or not you see these spaces depends upon which editor you use and what you do to get the file to the editor.
If the file is variable length, the trailing spaces will be there if you put them there. Whether or not you see these spaces depends upon which editor you use and what you do to get the file to the editor.
For example, if you FTP the file from the mainframe to your PC, then open it with a PC editor -- the spaces may not be there anymore since FTP has an option to remove trailing spaces from each record while transferring them. The spaces are still in the file on the mainframe, of course, but you cannot see them due to the way you transferred the file to your editor.