Angular 8 - send file as byte[] - file

Question

My case is to send a file to the backend but the only file content as byte array eg:
public saveFile(file: File, name: string, description: string): Observable<SymbolResponseEditModel> {
let formData: FormData = new FormData();
formData.append('FileName', name);
formData.append('FileDescription', description);
formData.append('Attachment', file); // <--- this must be a byte array instead of File
return this.http.post<SymbolResponseEditModel>(
'http://senddata.com',
formData
);
Result of this code is that I send to the backend a file containing additional information at the begining
a file containing additional information at the begining as you can see on the picture.
To do this I try to convert the file using file reader but I cannot convert a file to bytearray according to: Getting byte array through input type = file
var reader = new FileReader();
reader.onload = function() {
var arrayBuffer = this.result,
array = new Uint8Array(arrayBuffer),
binaryString = String.fromCharCode.apply(null, array);
console.log(binaryString);
}
reader.readAsArrayBuffer(this.files[0]);
And the error
TS2345: Argument of type 'File' is not assignable to parameter of type 'ArrayBuffer | SharedArrayBuffer | ArrayLike<number>'.
Type 'File' is missing the following properties from type 'SharedArrayBuffer': byteLength, length, [Symbol.species], [Symbol.toStringTag]
The second idea is to remove two lines from the file while downloading because the reasponse content type is octet-stream:
const reader = new FileReader();
reader.addEventListener('loadend', (e) => {
const text = e.srcElement.result; // <-- this text is encoded but I don't want it. Anyway the file is different than I
// sent and i am not able to read it.
let splittedString = text.split('\n');
splittedString = splittedString.splice(2);
let concatenedArray = splittedString.join('\n');
this.fetch(concatenedArray, symbolName);
});
reader.readAsArrayBuffer(response);
This whould work but the reader encode the file.
Have you got any other idea how to send a file as byte array without additional information? Is it possible?