You can reference the DOM Element using ElementRef and then extract the data of the file uploaded from the element reference. Use #variableName to reference the file input.

<input #fileInput (change)="fileUpload()" type="file" name="pic" accept="image/*">

In your component class, reference the file input using ViewChild.

import {Component, ElementRef, Renderer2, ViewChild} from '@angular/core'
@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>{{name}}</h2>
      <input #fileInput (change)="fileUpload()" type="file" name="pic" accept="image/*">
    </div>
  `,
})
export class App {
  name:string; 
  @ViewChild('fileInput') el:ElementRef;
  constructor(private rd: Renderer2) {
    this.name = `Angular : File Upload`
  }

  fileUpload() {
    console.log(this.el);
    // Access the uploaded file through the ElementRef
    this.uploadedFile = this.el.nativeElement.files[0]; 

  }
}

I have created a sample plunker here.

Why don't you use directive with change event?

component.html

<input type='file' uploader accept=".txt,.doc">

uploader.directive.ts

import { Directive, HostListener } from '@angular/core';

@Directive({
  selector: '[uploader]'
})
export class UploaderDirective {

  @HostListener('change',['$event.target.files'])
  onChanges(files) {
    this.readFile(files[0])
  }

  readFile(file){
    let fileReader = new FileReader();
    fileReader.onload = async (e: any) => {
      //DO SOMETHING HERE with e.target.result            
    }
    fileReader.readAsText(file);         
  }

}

Don't forget to add the Directive to your module.