How to specify resolution (px/inch) when creating new PDF content?

Is there a way to detect what resolution a PDF is at (px/inch) or a way
to specify resolution when creating a new PDF using the PDFTron API?

PDFNet SDK is using the standard PDF/PostScript units called points.
One point is 1/72 of an inch.

When you place images on the page (as illustrated in AddImage sample
project) you are specifying image dimensions in points.
The image DPI (dots per inch) is specified implicitly. For example, if
the image is 1000 pixels wide and the image element is 100 points wide,
the image DPI is 1000 pixels / 100 points = 10 pixel per point = 10 *
72 DPI = 720 DPI.

A similar calculation can also be used to find the dimensions for the
image element in order to match a predefined DPI value: image width
(in points) = pixel width / (dpi * 72)