When you use FileOpen() it returns the HANDLE data type which you can use in other local functions to read, write, and update the file. SYS_FileOpen() also returns a HANDLE data type which you can use with remote file handles. The only difference between FileOpen() and SYS_FileOpen() is where the file that is opened resides. FileOpen() opens a file locally on the "host" (partner.exe). If you are using distributed testing, you may want to open a file on the "target" or remote machine. In that case, you must use SYS_FileOpen() to open the remote file and then use the appropriate SYS_ file manipulation function to complete the task.
If you open a file locally with FileOpen(), you must use local file functions (such as FileReadLine and FileWriteLine). You cannot use remote functions, such as SYS_FileReadValue. If you open a file on a target machine with SYS_FileOpen(), you must use SYS_ functions (such as SYS_FileReadLine and SYS_FileWriteLine) to edit it.