There is Custom Service in the backend, When I Upload a file to the attachments, at the same time the file should also be sent to Custom Service. I am not able to get the uploaded file. Is there any handler that deals with this.
In this situation, it would be better to create your own handler for the file upload.
For example, you can add it on the "After record added" event to the [Object]File object in the configuration. There you will call your service and you would be able to get all the necessary columns from the file.
Also, take a look at the upload method in the schema FileDetailV2. from there you can also get information about the file.