1 const onDrop = async (index, acceptedFiles) => {
2   .
3   .
4   .
5 }
6 
7  <Dropzone onDrop={acceptedFiles =>onDrop(1,acceptedFiles )} accept=".pdf" maxSize={50000000}>

1onDrop(accepted, rejected, myArgument) {
2  console.log(accepted, rejected, myArgument)
3}
4
5<Dropzone onDrop={(accepted, rejected) => {this.onDrop(accepted, rejected, 'third')}}>
6  <p>Drop files here...</p>
7</Dropzone>