What could be the cause for remote data corruption when using the google drive android API?

 @Override
    @SuppressLint("NewApi")
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == CropImage.PICK_IMAGE_CHOOSER_REQUEST_CODE) {
            if (resultCode == Activity.RESULT_OK) {


             Uri mUri = CropImage.getPickImageResultUri(this, data);

             writeStreamToFile(getApplicationContext(),mUri,".pdf");

            }
        }
    }

   @RequiresApi(api = Build.VERSION_CODES.KITKAT)
    void writeStreamToFile(Context mContext, Uri mUri,String ext) {
        if (mUri == null) {
            return;
        }

        String[] filePathColumn = {MediaStore.Images.Media.DATA};

        Cursor cursor = mContext.getContentResolver().query(mUri, filePathColumn, null, null, null);
        String mCurrentPath = null;
        if (cursor != null && cursor.moveToFirst()) {
            int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
            mCurrentPath = cursor.getString(columnIndex);
            cursor.close();
        }

        if (TextUtils.isEmpty(mCurrentPath)) {
            mCurrentPath = mUri.getPath();
        }

        File storageDir = mContext.getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS);
        InputStream inputStream = null;
        try {
            inputStream = mContext.getContentResolver().openInputStream(mUri);

            File file = File.createTempFile("pptFiles", ext, storageDir);

            try (OutputStream output = new FileOutputStream(file)) {
                byte[] buffer = new byte[4 * 1024]; // or other buffer size
                int read;
                while ((read = inputStream.read(buffer)) != -1) {
                    output.write(buffer, 0, read);
                }
                output.flush();
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }