Set PNG transparency support.
[read/write property] pngTransparency([out, retval] VARIANT_BOOL *transparency) pngTransparency([in] VARIANT_BOOL transparency)
This property enables (if true) or disables (if false) generation of an alpha channel in PNG output. The default is disabled.

If transparency is enabled, the PDF rasterizer will be configured to skip the final compositing step (with an opaque background paper color).

NOTE: Transparent PNG output is only useful with PDF files that have been constructed with a transparent background. This parameter is only relevant when writePageBitmap or writeRegionBitmap is called with imageFilePNG.

The resetParams function resets PNG transparency to the default value of disabled.

pdf.pngTransparency = True