pdf to gbr conversion is always searched in the context of Gerber / PCB files, in particular for options on how to recover previously exported technical designs from PDB files back to GBR format.
Not easy, but not impossible, and certainly not perfect. You can find dedicated utilities for this, such as pdf2gerb, but most users do it manually.
This workaround consists of exporting the graphics from PDF format to SVG format and importing that to Gerber software in order to manually recreate the design.
Updated: January 23, 2024