Progect/AddEditPage.xaml

<Page x:Class="WpfApp1.AddEditPage"
      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:local="clr-namespace:WpfApp1"
      mc:Ignorable="d" 
      d:DesignHeight="450" d:DesignWidth="800"
      Title="AddEditPage">

    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="200"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="32"/>
            <RowDefinition Height="32"/>
            <RowDefinition Height="32"/>
            <RowDefinition Height="32"/>
            <RowDefinition Height="32"/>
            <RowDefinition Height="64"/>
        </Grid.RowDefinitions>
        <TextBlock Text="Пароль" HorizontalAlignment="Center" Margin="4"/>
        <TextBlock Text="Фамилия" Grid.Row="1" HorizontalAlignment="Center" Margin="4"/>
        <TextBlock Text="Имя" Grid.Row="2" HorizontalAlignment="Center" Margin="4"/>
        <TextBlock Text="Отчество" Grid.Row="3" HorizontalAlignment="Center" Margin="4"/>
        <TextBlock Text="Логин" Grid.Row="4" HorizontalAlignment="Center" Margin="4"/>
        <TextBox Text="{Binding Password}" MaxLength="50" Grid.Column="1" Margin="4,4,70,4"/>
        <TextBox Text="{Binding FirstName}" MaxLength="100" Grid.Column="1" Grid.Row="1" Margin="4,4,70,4"/>
        <TextBox Text="{Binding MiddleName}" MaxLength="50" Grid.Column="1" Grid.Row="2" Margin="4,4,70,4"/>
        <TextBox Text="{Binding LastName}" MaxLength="100" Grid.Column="1" Grid.Row="3" Margin="4,4,70,4"/>
        <TextBox Text="{Binding Login}" MaxLength="15" Grid.Column="1" Grid.Row="4" Margin="4,4,500,4"/>

        <Button Content="Сохранить" Grid.ColumnSpan="2" Grid.Row="5" Name="BtnSave" Click="BtnSave_Click"></Button>
    </Grid>
</Page>