Simple answer: Don't.
The user control should not know or care about the page that contains it. It should be entirely self-contained.
Instead, have the user control raise an event when the parent grid should be bound. The containing page can then subscribe to that event, and do whatever it needs to when the event is raised.
User control:
using System;
partial class UserControls_ManageDocument : System.Web.UI.UserControl
{
public event EventHandler BindGrid;
protected void btnSave_Click(object sender, EventArgs e)
{
if (some conditions)
{
EventHandler handler = BindGrid;
if (handler != null) handler(this, EventArgs.Empty);
}
}
}
Parent page:
<uc1:Document runat="server"
OnBindGrid="BindGrid"
/>
protected void BindGrid(object sender, EventArgs e)
{
}