Then you're not looking for a newsletter posting system.
You want someone to click a link on a PDF that goes back to your internal IIS site with a piece of code that says "User XYZ read it" and have that stored in a database.
So this begs to question. What is your server environment like. Do you even have a server?
Code:
<%
strConn = "your connection string here"
Set cn = Server.CreateObject("ADODB.Connection")
cn.Open strConn
Set rs = Server.CreateObject("ADODB.Recordset")
rs.Execute("insert into yourtable (user,whenread) values ('" & request("user") & "',now())",cn)
cn.Close
%>
Then in your PDF link:
http://yourserver/readuser.asp?user=UserNameThatOpened
Won't work perfectly since the PDF will probably not be able to contain the recipient, but, again, depending on your server enviroment, if you use Active Directory etc, you'd need to make adjustments for it.
Where is your IT team?