convertToPdfPoint(x, y) {
    const p = [x, y];
    Util.applyInverseTransform(p, this.transform);
    return p;
  }
Converts viewport coordinates to the PDF location. For examples, useful
for converting canvas pixel location into PDF one.
@param {number} x - The x-coordinate.
@param {number} y - The y-coordinate.
@returns {Array} Array containing `x`- and `y`-coordinates of the
  point in the PDF coordinate space.
@see {@link convertToViewportPoint}