https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.scrollablecontrol.setautoscrollmargin?view=netframework-4.8.1&tree=cete.dynamicpdf.viewer.pdfnavigationpanel.setautoscrollmargin
ScrollableControl.SetAutoScrollMargin(Int32, Int32) Method (System.Windows.Forms) | Microsoft Learn
Sets the size of the auto-scroll margins.
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