iText7 - create PDF with exact dimensions when printed - how?

Question

I'm creating a simple PDF using iText7 (C#) but I need it to be printed at exactly the right size. Here's my code:

        PdfWriter writer = new PdfWriter("output.pdf");
        PdfDocument pdf = new PdfDocument(writer);
        pdf.SetDefaultPageSize(iText.Kernel.Geom.PageSize.LETTER);
        var page = pdf.AddNewPage();
        page.SetCropBox(new iText.Kernel.Geom.Rectangle(36, 36, 7.5f * 72, 10 * 72));
        PdfCanvas canvas = new PdfCanvas(page);
        canvas.SetStrokeColor(ColorConstants.BLACK).SetLineWidth(3);
        canvas.MoveTo(36, 36);
        canvas.LineTo(36, 36 + 72);       // Draw a line 1 inch long
        canvas.LineTo(36 + 72, 36 + 72);  // Draw a second line, perpendicular to the first, also 1 inch long
        canvas.ClosePathStroke();
        pdf.Close();

If I right-click the resulting PDF and select "Print", my triangle is off the bottom of the page.

When I open the resulting PDF in the PDF program I'm using (PDF Architect), it gives me a few options:

If I just click "Print", it gives me lines that are 1 1/16" long and start about 1/8" from the edge of the page, so by default PDF Architect seems to be taking the contents of my crop box and expanding it to the maximum page availability.

If I click on "Fit" before clicking "Print", that results in the desired output - lines 1" long, starting 1/2" from each side of the page. That works but is error-prone - too easy to forget to click "Fit" every time.

Is there a way to generate a PDF that contains information that says "I'm targeting this document at letter size, but I'm staying 1/2" away from all the edges, so when you print, if the printer has margins <= 1/2 inch you should be fine, and just print it exactly how I've described without any shrinking or enlarging"?

Answer 1

You will not be able to completely control this from the PDF document. The PDF processor (e.g. viewing application) or the printer (driver) will always be able to scale the content up or down.

Apparently, PDF Architect has the "Fit" option enabled by default, so it scales the page to the selected paper size.
You are setting a crop box of 7.5x10 in. I assume you're printing to Letter sized (8.5x11 in) paper. So the 7.5x10 page will indeed be scaled up, and your content will become slightly larger.

Is there a way to generate a PDF that contains information that says "I'm targeting this document at letter size, but I'm staying 1/2" away from all the edges, so when you print, if the printer has margins <= 1/2 inch you should be fine, and just print it exactly how I've described without any shrinking or enlarging"?

I would not set the crop box. When the pages in the PDF document are Letter size and the output paper is also Letter size, it should not matter whether the "Fit" option is enabled or not, as not scaling needs to happen. It's definitely not a fool proof solution, but at least it's less error prone.