Hi @jefrii
In short if i need to explain the use of these activities would be :
File Transfer: To transfer, Download files from our remote SFTP server to an external server. It can also be used to check the existence of the files. You can refer the documentation here.
File Collector: It is used to collect/download files from the application server or the server on which wfserver module is running. You can refer the documentation here.
Thanks
Akshay