There is opportunity to further optimize the caching mechanism of the image sources, which will reduce the memory consumption. The fast scrolling in a document containing big images could lead to an OutOfMemoryException.
Openining very large images as well. 

To reproduce: please run the attached sample project. If you reload the document, the horizontal scrollbar is not shown.

Workaround:
        public RadForm1()
        {
            InitializeComponent();

            this.radPdfViewer1.FitToWidth = false;
            this.radPdfViewer1.ViewerMode = Telerik.WinControls.UI.FixedDocumentViewerMode.None;
            this.radPdfViewer1.EnableThumbnails = false; 
            this.radPdfViewer1.DocumentLoaded += radPdfViewer1_DocumentLoaded;
            this.radPdfViewer1.LoadDocument(@"..\..\Go Air - Himanshe Ajeet Dubey - 17-01-2018 - Ranchi to Mumbai.pdf");
            Application.DoEvents();
        }

        private void radPdfViewer1_DocumentLoaded(object sender, EventArgs e)
        {
            Application.DoEvents();
            this.radPdfViewer1.FitToWidth = true;
        }

Load a file in RadPdfViewer, select some of the text, right click and select Copy. A sample pdf file is attached.

It will be a great addition of RadPdfViewer if it supports forms/controls.

The events should provide information as to when a page is about to be rendered and when it is displayed in the control.

How to reproduce: check the attached project

Workaround: manually unload the document before disposing the control, the attached project includes a solution

This functionality should be similar to the one provided by Adobe.

The PdfPrintPreviewDialog should allow the end user to resize it and the page preview in it should scale accordingly. This would allow the user to have a better preview of the print settings.

Include Marquee Zoom as tool.

This dialog appears when one is clicking the signature field in the document.