I think the issue you're seeing is because the font used in the generated PDF file is not the same as the font specified in the figure.
In the example figure you posted, both the title and the legend are using Calibri as the font. The exported PDF file uses Courier instead.
MATLAB supports a small set of fonts when exporting to PDF and PostScript, and Calibri is not one of the fonts that is supported. If the font isn't supported a substitution occurs when exporting, and in this case Courier is being used.
If you set the axes and legend text to use Helvetica instead you should see better results.
set(ax, 'FontName', 'Helvetica');
set(leg, 'FontName, 'Helvetica');