How to create a blank PDF in C#

The shortest working example

If you just need a blank PDF with the default first page, create it and save it.

using ZingPDF;

using var pdf = Pdf.Create();
using var output = File.Create("blank.pdf");

await pdf.SaveAsync(output);

Set the page size when you create the document

If you already know the page size you want, set the media box during creation.

using ZingPDF;
using ZingPDF.Syntax.CommonDataStructures;

using var pdf = Pdf.Create(options =>
{
    options.MediaBox = Rectangle.FromDimensions(595, 842);
});

await pdf.SaveAsync(File.Create("a4-blank.pdf"));

That keeps the first page aligned with the output you want instead of creating a default page and changing it later.

Add more pages before you save

A new document starts with one page, so call AppendPageAsync(...) when you need more.

using var pdf = Pdf.Create(options =>
{
    options.MediaBox = Rectangle.FromDimensions(595, 842);
});

await pdf.AppendPageAsync();
await pdf.AppendPageAsync();

await pdf.SaveAsync(File.Create("three-pages.pdf"));