In the PDF document all objects which look like letters/text are, in reality, character commands. Take, for example, an ‘i’:

Instead of the command ‘Text output:i’ in the PDF source text, the instructions: ‘Draw a point’ and ‘Draw a short vertical line’ are issued. If there are no text output instructions in the PDF document, no text entities will be generated in the DXF. Character instructions will be exported as character entities and text output instructions as text entities. Changing the preferences for the text output has no influence upon this, this is also true for the preference that no texts are to be exported.