WPF DocumentViewer control loses icons when changing template, how to show icons - xaml

Question

I am tryng to add 2 new buttons to a document viewer control that us then hosted in a windows form, so I took the template from MSDN to modify, but the all the "inbuilt" standard buttons turn to text on display rather than the icons. I am wondering if anyone can please help me with why this happens and how to fix it as I have not been able to determine that from MSDN documentation. However I am a newbie to XAML. Below is the xaml for the modified control.
<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:Documents="clr-namespace:System.Windows.Documents;assembly=PresentationUI" x:Class="AddinXPSViewer.XPSBrowser"
xmlns:self="clr-namespace:AddinXPSViewer"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
>
<Frame x:Name="DocFrame">
<Frame.Content>
<Grid>
<DocumentViewer x:Name="docViewer" HorizontalAlignment="Left" VerticalAlignment="Bottom" Margin="0,0,0,0" Unloaded="docViewer_Unloaded" Style="{DynamicResource DocumentViewerStyle}" ContextMenu="{x:Null}" >
<DocumentViewer.Resources>
<Style x:Key="DocumentViewerStyle" TargetType="DocumentViewer">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}"/>
<Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
<Setter Property="FocusVisualStyle" Value="{x:Null}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="DocumentViewer">
<Grid KeyboardNavigation.TabNavigation="Local">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<ToolBar
ToolBarTray.IsLocked="True"
KeyboardNavigation.TabNavigation="Continue">
<Button Command="ApplicationCommands.Copy"
CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
Content="Copy"/>
<Separator />
<Button Command="NavigationCommands.IncreaseZoom"
CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
Content="Zoom In"/>
<Button Command="NavigationCommands.DecreaseZoom"
CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
Content="Zoom Out"/>
<Separator />
<Button Command="NavigationCommands.Zoom"
CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
CommandParameter="100.0"
Content="Actual Size" />
<Button Command="DocumentViewer.FitToWidthCommand"
CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
Content="Fit to Width" />
<Button Command="DocumentViewer.FitToMaxPagesAcrossCommand"
CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
CommandParameter="1"
Content="Whole Page"/>
<Button Command="DocumentViewer.FitToMaxPagesAcrossCommand"
CommandTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"
CommandParameter="2"
Content="Two Pages"/>
<Button Command="self:XPSBrowserCustomCommands.Next">Previous</Button>
<Button Command="self:XPSBrowserCustomCommands.Previous">Next</Button>
</ToolBar>
<ScrollViewer Grid.Row="1"
CanContentScroll="true"
HorizontalScrollBarVisibility="Auto"
x:Name="PART_ContentHost"
IsTabStop="true"/>
<ContentControl Grid.Row="2"
x:Name="PART_FindToolBarHost"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</DocumentViewer.Resources>
<DocumentViewer.CommandBindings>
<CommandBinding Command="ApplicationCommands.Print" Executed="CommandBinding_OnPrint" />
<CommandBinding Command="ApplicationCommands.Print" CanExecute="CommandBinding_CanExecutePrint" />
<CommandBinding Command="self:XPSBrowserCustomCommands.Next" Executed="CommandBinding_OnPrevious" />
<CommandBinding Command="self:XPSBrowserCustomCommands.Next" CanExecute="CommandBinding_CanExecutePrevious" />
<CommandBinding Command="self:XPSBrowserCustomCommands.Previous" Executed="CommandBinding_OnNext" />
<CommandBinding Command="self:XPSBrowserCustomCommands.Previous" CanExecute="CommandBinding_CanExecuteNext" />
</DocumentViewer.CommandBindings>
</DocumentViewer>
</Grid>
</Frame.Content>
</Frame>
</UserControl>

Answer 1

The secret is to right click and edit the Template or a copy of the Template twice in visual studio, this gives a different template to the one on msdn, and access to the sub controls for the toolbar.

Answer 2

On each Button the Content property is set to a string value.
e.g. Content="Copy"
If you want it to be an image you will have to set it to an Image control.
e.g.
<Button>
<Image Source="copy.png"/>
</Button>
The 'default templates' on MSDN are not the actual default templates from WPF. They are just sample code for making your own control template.