Workaround: manually increase the font of the controls

protected override void OnShown(EventArgs e)
{
    base.OnShown(e);

    var dpi = NativeMethods.GetSystemDpi();

    this.Font = new Font(this.Font.Name, this.Font.Size * dpi.X / 96, this.Font.Style);
    this.radMenu1.Font = new Font(this.radMenu1.Font.Name, this.radMenu1.Font.Size * dpi.X / 96, this.radMenu1.Font.Style);
    this.radCommandBar1.Font = new Font(this.radCommandBar1.Font.Name, this.radCommandBar1.Font.Size * dpi.X / 96, this.radCommandBar1.Font.Style);
}

Workaround:

            this.radChat1.ChatElement.InputTextBox.TextBoxItem.TextBoxControl.Multiline = true;
            this.radChat1.ChatElement.InputTextBox.ButtonsStack.Children.Remove(this.radChat1.ChatElement.ShowToolbarButtonElement);
            this.radChat1.ChatElement.InputTextBox.ButtonsStack.Children.Remove(this.radChat1.ChatElement.SendButtonElement);
            StackLayoutElement stack = new StackLayoutElement();
            stack.MinSize = new Size(0, 60);
            this.radChat1.ChatElement.InputTextBox.Parent.Children.Add(stack);
            this.radChat1.ChatElement.InputTextBox.Parent.Children.Remove(this.radChat1.ChatElement.InputTextBox);
            stack.StretchHorizontally = true;
            stack.Orientation = Orientation.Horizontal;
            stack.Children.Add(this.radChat1.ChatElement.InputTextBox);
            stack.Children.Add(this.radChat1.ChatElement.ShowToolbarButtonElement);
            stack.Children.Add(this.radChat1.ChatElement.SendButtonElement);
            this.radChat1.ChatElement.ShowToolbarButtonElement.StretchHorizontally = false;
            this.radChat1.ChatElement.SendButtonElement.StretchHorizontally = false;

Added in the R3 2018 release: https://docs.telerik.com/devtools/winforms/forms-and-dialogs/form-converter

Workaround: 

Import using a stream.

Note: other operations that affect the image's size should also handle large images.

No Workaround.

It is possible to create a custom resize dialog as follows:
        public class MyRadImageEditor : RadImageEditor
        {
            protected override RadImageEditorElement CreateImageEditorElement()
            {
                return new MyRadImageEditorElement();
            }
        }

        public class MyRadImageEditorElement : RadImageEditorElement
        {
            public override void ShowResizeDialog()
            {
                this.ShowDialog(typeof(MyResizeDialog));
            }
        }

        public class MyResizeDialog : RadForm
        {
            public MyResizeDialog(RadImageEditorElement imageEditorElement)  
            {
               
            }

            //TODO custom dialog
        }

To reproduce:
public RadForm1()
{
    InitializeComponent();
    var a = new Author(null, "John");
    for (int i = 0; i < 20; i++)
    {
        radChat1.AddMessage(new ChatTextMessage("Item" + i, a, DateTime.Now.AddDays(-(20 - i))));
    }
    new Telerik.WinControls.RadControlSpy.RadControlSpyForm().Show();

    this.radChat1.ChatElement.MessagesViewElement.TimeSeparatorInterval = TimeSpan.FromDays(1);
}

You will notice that there is today in several places. 

Workaround:
this.radChat1.ChatElement.MessagesViewElement.TimeSeparatorInterval = TimeSpan.Zero;

var a = new Author(null, "Forest Gump");
for (int i = 0; i < 20; i++)
{
    radChat1.AddMessage(new ChatTextMessage("Item" + i, a, DateTime.Now.AddDays(-(20 - i))));

    ChatTimeSeparatorDataItem separator = new ChatTimeSeparatorDataItem(new ChatTimeSeparatorMessage(DateTime.Now.AddDays(-(20 - i))));
    radChat1.ChatElement.MessagesViewElement.Items.Add(separator);
}

How to reproduce: 
1. Use the following code to change the default style of the document:
StyleDefinition h2 = this.radRichTextBox.Document.Style;
h2.SpanProperties.FontFamily = new System.Windows.Media.FontFamily("Microsoft Sans Serif");
h2.SpanProperties.FontSize = Unit.PointToDip(8.25f);
h2.ParagraphProperties.SpacingAfter = 0;

h2 = radRichTextBox.Document.Style;
h2.SpanProperties.FontFamily = new System.Windows.Media.FontFamily("Microsoft Sans Serif");
h2.SpanProperties.FontSize = Unit.PointToDip(8.25f);
h2.ParagraphProperties.SpacingAfter = 0;

StyleDefinition hyperlinkStyle = this.radRichTextBox.Document.StyleRepository["Hyperlink"];
hyperlinkStyle.SpanProperties.FontFamily = new System.Windows.Media.FontFamily("Microsoft Sans Serif");
hyperlinkStyle.SpanProperties.FontSize = Unit.PointToDip(8.25f);

2. Add some text to the document

3. Add a hyperlink somewhere in the middle of the text

4. Start moving the caret so it moves over the hyperlink start

Observed: When on hyperlink start/end, the caret is with bigger size than the content

Expected: The caret should be with the size of the content

Workaround: create the ThemableColor this way

SetBordersCommandParameter bordersParam = new SetBordersCommandParameter();
System.Drawing.Color color = Color.Blue;
System.Windows.Media.Color mediaColor = System.Windows.Media.Color.FromArgb(color.A, color.R, color.G, color.B);
bordersParam.BorderColor = new ThemableColor(mediaColor);

How to reproduce:
this.radTrackBar1.LabelStyle = Telerik.WinControls.UI.TrackBarLabelStyle.TopLeft;
this.radTrackBar1.TickStyle = Telerik.WinControls.Enumerations.TickStyles.TopLeft;

Workaround:
this.radTrackBar1.LabelStyle = Telerik.WinControls.UI.TrackBarLabelStyle.TopLeft;
this.radTrackBar1.TrackBarElement.BodyElement.ScaleContainerElement.BottomScaleElement.Visibility = ElementVisibility.Collapsed;

How to reproduce: test the attached project with the latest version on a Windows 7 machine, notice that the font sizes are scaled, test the project with assemblies before  R2 2017 the fonts are not scaled

The issue is observed even with the RadControl.EnableDpiScaling property set to false. It would be expected that if the property was set to false, that the fonts would not be increased.

Workaround: change the fonts for each of the controls individually, the scaling can be calculated this way:
  Protected Overrides Sub OnShown(e As EventArgs)
        MyBase.OnShown(e)

        Dim dpi = NativeMethods.GetSystemDpi()
        Dim scale = dpi.X / 96.0
    End Sub

To reproduce: please refer to the attached sample project and gif file.

Workaround: use screentips: https://docs.telerik.com/devtools/winforms/telerik-presentation-framework/tooltips-and-screentips/screen-tips

How to reproduce: check the attached video
Workaround: select a color from a different tab or use the color picker

How to reproduce: enabled High DPI scaling and create a form as an MDI child with a RadDataEntry control in it
Workaround:  handle the Shown event of the MDI child and manually perform the scaling
private void radButtonElement1_Click(object sender, EventArgs e)
        {
            var view = new RadForm1
            {
                MdiParent = this
            };
            
            view.Shown += View_Shown;
            view.Show();
        }

        private void ScaleRadControls(Control c)
        {
            foreach (var item in c.Controls)
            {
                Control control = item as Control;
                if (control == null)
                {
                    continue;
                }

                this.mi.Invoke(control, new object[] { this.FormElement.DpiScaleFactor, BoundsSpecified.All });
                ScaleRadControls(control);
            }
        }

        MethodInfo mi;
        private void View_Shown(object sender, EventArgs e)
        {
            this.mi = typeof(Control).GetMethod("ScaleControl", BindingFlags.Instance | BindingFlags.NonPublic, null, new Type[] { typeof(SizeF), typeof(BoundsSpecified) }, null);
            RadForm1 v = sender as RadForm1;
            if (v != null)
            {
                ScaleRadControls(v.radDataEntry1.PanelContainer);
            }
        }

To reproduce:
- Open the Element Hierarchy Editor and resize it.

http://demos.telerik.com/aspnet-ajax/treelist/examples/overview/defaultcs.aspx