GeoPDF is a trade mark of TerraGo and only programs which are licensed by TerraGo can create GeoPDF (tm) files.
There are two systems to encode georeferencing in PDF and they are documented in http://www.gdal.org/frmt_pdf.html. Alternatives are ISO32000 or OGC Best Practice. GDAL can write the both variants if desired with a creation option parameter:
GEO_ENCODING=[NONE/ISO32000/OGC_BP/BOTH]: Set the Geo encoding method
to use. ISO32000 is the default.
Your command is is using the default one while GeoPDF (tm) is using the OGC_BP one which means that TerraGo toolbar will not recognize the PDF as GeoPDF (tm). Unfortunately running the conversion with creation option parameter will not change anything for you.
The reason is that TerraGo has changed its policy with openness and new TerraGo program versions accept only those PDF files which are created with licensed TerraGo products. So even GDAL can write the georeferencing in the GeoPDF (tm) way the TerraGo Toolbar will not show the coordinates for the users.
Even if you could make TerraGo toolbar to read the coordinates you could not start drawing because GDAL can't set PDF into editable. You would need to open the PDF first for example with Adobe Illustrator for making it editable.