Can't import PDF library in Python mode

[AjitDingankar]

In Processing version 4.3.4 on Ubuntu 20.04, I can't import the PDF library in Python mode.
Tried the following variations:

# add_library('pdf')                         # Added by Processing in Python mode 
add_library('PDF')                           # Tried uppercase name 
# add_library('processing.pdf.*')            # Added by Processing and works in Java mode  
# add_library('processing.pdf.PGraphicsPDF') # Trying the specific name shown in error

They all throw the same error:

Please use Sketch → Import Library to add processing.pdf.PGraphicsPDF to your sketch.

Note that the following line added by Processing in Java mode works!

import processing.pdf.*;