The issue is reproducible only on Windows XP. On newer versions of windows, the images are rendered as expected.

WORKAROUND: You may try implementing custom filter that handles the CMYK scenario. How to implement custom DCTDecode filter is described in this documentation article:
https://docs.telerik.com/devtools/winforms/pdfviewer/customize-and-extensibility/customize-pdf-rendering

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);

According to PDF format specification, there are three valid encoding name values (MacRomanEncoding, MacExpertEncoding and WinAnsiEncoding). There are documents that instead of skipping the optional Encoding property, are writing invalid /NULL name value in the font dictionary. Currently, in this invalid document scenario RadPdfViewer throws and catches Exception and this results in missing text content. 

We may handle this invalid document scenario by ignoring the invalid Encoding value.

Add functionality for a PDF form filler that supports text auto-sizing/shrinking like Adobe:

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,

Import documents that use this type of encryption. Currently, a handled NotSupportedEncryptionException with message "The encryption method with code 5 is not supported." is thrown while importing such a document.

This is Unicode (UTF-16BE) encoding for the Adobe-GB1 character collection; contains mappings for all characters in the GB18030-2000 character set.

Described on page 443 in Pdf Reference 1.7.