To reproduce:

  doc.Pages[0].CropBox = new Rect(150, 150, doc.Pages[0].Size.Width - 30, doc.Pages[0].Size.Height - 30);

Is there a way to load this RadFixedDocument into a RadPdfViewer without writing the document to a file first and then loading it in the viewer?

Workaround:

You can achieve the desired functionality by exporting the RadFixedDocument to a MemoryStream instead of a file in the file system and then load it in the PdfViewer: 

RadFixedDocument document = CreateRadFixedDocument();

PdfFormatProvider pdfFormatProvider = new PdfFormatProvider();
Stream ms = new MemoryStream();
pdfFormatProvider.Export(document, ms);

radPdfViewer1.LoadDocument(ms);

Hi,

Is there a way to get version and producer metadata from imported PDF files? 

Here is how it looks in AdobeReader

Thanks in advance,

This is the result with R3 2022:

This is the result with R2 2023 SP1: