1. Simply change the contenttype and open the PDF file

Response.Clear();
Response.ContentType = "application/pdf"; //change the content here based on different files type
Response.AddHeader("Content-Disposition", "inline;filename=" + strFilePath);
Response.WriteFile(strFilePath);
Response.End();

2. use Iframe Html control, set the src attribute of the control as PDF file and thats it..

Following is a ASP.net server control which uses the iframe,

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace PdfViewer
{
    [DefaultProperty("FilePath")]
    [ToolboxData("<{0}:ShowPdf runat=server></{0}:ShowPdf>")]
    public class ShowPdf : WebControl
    {
        #region "Declarations"

        private string mFilePath;

        #endregion
        #region "Properties"

        [Category("Source File")]
        [Browsable(true)]
        [Description("Set path to source file.")]
        [Editor(typeof(System.Web.UI.Design.UrlEditor),
            typeof(System.Drawing.Design.UITypeEditor))]

        public string FilePath
        {
            get
            {
                return mFilePath;
            }

            set
            {
                if (value == string.Empty)
                {
                    mFilePath = string.Empty;
                }
                else
                {
                    int tilde = -1;
                    tilde = value.IndexOf('~');

                    if (tilde != -1)
                    {
                        mFilePath = value.Substring((tilde + 2))
                                         .Trim();
                    }
                    else
                    {
                        mFilePath = value;
                    }
                }
            }
        }   //end FilePath property

        #endregion

        #region "Rendering"

        protected override void RenderContents(HtmlTextWriter writer)
        {
            try
            {
                StringBuilder sb = new StringBuilder();

                sb.Append("<iframe src="
                          + FilePath.ToString() + " ");

                sb.Append("width=" +
                          Width.ToString() + " height=" +
                          Height.ToString() + " ");

                sb.Append("<View PDF: <a href=" + FilePath.ToString() + "</a></p>");

                sb.Append("</iframe>");

                writer.RenderBeginTag(HtmlTextWriterTag.Div);

                writer.Write(sb.ToString());

                writer.RenderEndTag();
            }
            catch
            {

                // with no properties set, this will render
                // "Display PDF Control" in
                // a box on the page

                writer.RenderBeginTag(HtmlTextWriterTag.Div);

                writer.Write("Display PDF Control");

                writer.RenderEndTag();
            }  // end try-catch

            //end RenderContents

        #endregion

        }
    }
}

Refer the above control in WebPage :
<%@ Register TagPrefix="PDF" Namespace="PdfViewer" Assembly="<yourAssemblyname>" %>

Reference:- http://www.codeproject.com/aspnet/EmbedPDFinWebpages.asp