Configuring figure properties for saving

I'm using the "saveas" function in my code to automatically save a figure as a PDF file during a script. However, I cannot seem to set resolution, size and line weight properties for this.

When saving a single figure, I'd normally go into the Export Setup window from the File menu and set the required parameters (size as required, resolution to 300dpi, line weight to 4pt.) and the image would save accordingly. However, as I'm using "saveas" in a script to save a large number of figures in one go, I cannot seem to set these properties. I've tried setting them in the Export Setup window and saving as "default" but this has no effect.