Convert filelist to json format in angular 8

Question

Convert filelist into JSON format so that it can be passed as a JSON object along with other data from angular 8 to .net core web api controller.

API call from angular

 uploadFiles(document: Document): Observable<Document> {           
 return this.http.post<Document>(environment.apiEndpoint +"/Upload", document) 
.pipe(catchError(this.handleError));

}

model in angular

export class Document {
id: string;
name: string;
files: string;
}

HTML

           <div class="row">
                <div class="col-md-12">
                    <input type="file" id="file" accept=".pdf" name="fileInput" multiple
                        (change)="getFileDetails($event)">

                    <button type="button" class="btn btn-primary" (click)="uploadFiles()">Upload PDF(s)</button>
                </div>
            </div>

.ts

getFileDetails(event)
{   
this.file = event.target.files;
}

uploadFiles() {
if (this.file.length === 0) {
  return;
}

var files = this.file;                         
this.document.files= Object.assign({},files);

var Data = { ...documentdata, files }
this.service.upload(Data).subscribe(
 --------
   ------)

filelist(this.file):

(2) [File, File] 

0: File {name: "PromoTest.pdf", lastModified: 1606692735736, lastModifiedDate: Fri Aug 30 2019 
01:44:19 GMT+1100 (Eastern Daylight Time), webkitRelativePath: "", size: 46471, …}

1: File {name: "viewdoctest1.pdf", lastModified: 1604532330799, lastModifiedDate: Mon Oct 25 2020 
12:02:25 GMT+1100 (Eastern Daylight Time), webkitRelativePath: "", size: 568912, …}length: 
2__proto__: Array(0)

suggestions I tried from google

a = Array.from(theFileList)
a = Array.prototype.slice.call(theFileList)
const fileListAsArray = Array.from(fileList)
const files = [...myFileList]

I have tried different suggestions from google, but everytime I pass it, I get a response code:400 (bad request error)

.net model.

public class UploadDocumentViewModel
{
 public string Id{ get; set; } 
 public string Name { get; set; } 
 public IEnumerable<IFormFile> Files { get; set; } 
} 

controller

    [HttpPost]
    [Route("Upload")]        
    public async Task<string> Upload([FromBody] UploadDocumentViewModel model)