Hi ,its working now,thanks for your support.

I first showed the form and then loaded the file.

Dim resources As System.Resources.ResourceManager = New System.Resources.ResourceManager(GetType(frmMain))
Dim pdf As New AxAcroPDFLib.AxAcroPDF
pdf.OcxState = CType(resources.GetObject("AxAcroPDF1.OcxState"), System.Windows.Forms.AxHost.State)

ChildForm.Show(DockPanel) 'This is the line i brought up
pdf.LoadFile("path_to_pdf")

ChildForm.Controls.Add(pdf)


Thanks
Selvam