So here I tried implementing the above functionality but only managed to fetch image files only through the gallery,fileExplorer and google photos, but I'm not able to find out a way to do the same for a third party library like the camscanner or officeLens

    private val IMAGE_PICK_CODE = 1000;
          private val PERMISSION_CODE = 1001;

 fab.setOnClickListener { view ->

            if (VERSION.SDK_INT >= VERSION_CODES.M){
                if (checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) ==
                    PackageManager.PERMISSION_DENIED){

                    val permissions = arrayOf(Manifest.permission.READ_EXTERNAL_STORAGE);
                    requestPermissions(permissions, PERMISSION_CODE);
                }
                else{
                    pickImageFromGallery();
                }
            }
            else{
                pickImageFromGallery();
            }
        }
    }
    private fun pickImageFromGallery() {
        val intent = Intent(Intent.ACTION_PICK)
        intent.type = "image/*"
        startActivityForResult(intent, IMAGE_PICK_CODE)
    }
    //
    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
        when(requestCode){
            PERMISSION_CODE -> {
                if (grantResults.size >0 && grantResults[0] ==
                    PackageManager.PERMISSION_GRANTED){
                    //permission from popup granted
                    pickImageFromGallery()
                }
                else{
                    //permission from popup denied
                    Toast.makeText(this, "Permission denied", Toast.LENGTH_SHORT).show()
                }
            }
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        if (resultCode == Activity.RESULT_OK && requestCode == IMAGE_PICK_CODE){
            imageView.setImageURI(data?.data)
        }
    }

manifest file

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.CAMERA"/>