Page orientation in xamarin

You have to add a ScrollView in your Page.

Place the code you want to 'scroll' within the ScrollView tag.

Here is an example with your code:

<StackLayout>

 <ScrollView>
   <StackLayout>
       <Label FontSize="Medium">Nome Fornecedor:</Label>
       <Entry x:Name="NomeForecedor"></Entry>
       <Label FontSize="Medium">Cidade Fornecedor:</Label>
       <Entry x:Name="CidadeForecedor"></Entry>
       <Label FontSize="Medium">CNPJ:</Label>
       <Entry x:Name="Cnpj"></Entry>
       <Label FontSize="Medium">Estado:</Label>
       <Entry x:Name="EstadoForecedor"></Entry>
   </StackLayout>

   <StackLayout Orientation="Horizontal">
        <Button x:Name="btnSalvar"   
            BackgroundColor="Azure" 
            Text="Salvar" 
            HorizontalOptions="FillAndExpand"></Button>
        <Button x:Name="btnCancelar" 
            BackgroundColor="Azure"
            Text="Cancelar" 
            HorizontalOptions="FillAndExpand"></Button>
      </StackLayout>
 </ScrollView>

</StackLayout>

If you want to show ScrollView only when the screen changes orientation, you can use the example below:

• Xamarin Forms Orientation

Maybe you should use a Relative Layout because depending on it may not be legal for the user to scroll on a signup screen. link