hDPI

Set the horizontal print resolution.
[read/write property] hDPI([out, retval] int *dpi) hDPI([in] int dpi)
This property sets the horizontal print resolution, in dots per inch (DPI).

Similarly, the vDPI property sets the vertical print resolution.

The horizontal and vertical resolutions are typically the same. (There are exceptions, such as some chart printers.)

resetParams resets this to its default value, which is to use the driver's default resolution.

VB6:
pdf.hDPI = 300 pdf.vDPI = 300
vDPI
resetParams