Open is an overridden procedure used to open the output destination for messages written using the logging intercept. 

Open allocates resources for the internal TIdStreamVCL instance used to write log messages the filename specified in Filename. 

When Filename does not already exist, it is created. For an existing file in Filename, the stream is positioned at its end to append new log messages. 

Use Close to free the internal TIdStreamVCL instance used to write log messages to the file specified in Filename. 

Open does not call the inherited method. 

Open cannot be called from within the form designer or IDE; it has no effect and the method is exited without performing any action.

TIdLogFile.Filename 

TIdLogFile.Close 

TIdLogBase.Open