code: func RegisterFile(fpdf *gofpdf.Fpdf, imgName string, options gofpdf.ImageOptions, tiffFileStr string) (info *gofpdf.ImageInfoType) {
  	var f *os.File
  	var err error
  
  	if fpdf.Ok() {
  		f, err = os.Open(tiffFileStr)
  		if err == nil {
  			info = RegisterReader(fpdf, imgName, options, f)
  			f.Close()
  		} else {
  			fpdf.SetError(err)
  		}
  	}
  	return
  }
docs: // RegisterFile registers a TIFF image, adding it to the PDF file but not
  // adding it to the page. imgName specifies the name that will be used in the
  // call to Image() that actually places the image in the document. options
  // specifies various image properties; in this case, the ImageType property
  // should be set to "tiff". The TIFF image is read from the file specified by
  // tiffFileStr.