You can use Asset for this set 0 and 1 and play on that.
Beginning of the process Set the Asset value as Zero.
Get the Asset value using Get Asset activity
Then Use If activity
GetAssetvariable = 0
Then → Check the file is exist the folder
If it is exist do the process that you want and at last Update Asset value into 1 in the orchestrator by using Set Asset activity.
If the file is not exist just Asset remained the same
Else → Nothing to do
Regards
Gokul