code: func (c *Files) GetPreview(in *GetPreviewInput) (out *GetPreviewOutput, err error) {
  	body, l, err := c.download("/files/get_preview", in, nil)
  	if err != nil {
  		return
  	}
  
  	out = &GetPreviewOutput{body, l}
  	return
  }
docs: // GetPreview a preview for a file. Currently previews are only generated for the
  // files with the following extensions: .doc, .docx, .docm, .ppt, .pps, .ppsx,
  // .ppsm, .pptx, .pptm, .xls, .xlsx, .xlsm, .rtf