I've gotten the app to run as a service.  In the OnStart I create a loop and
use thread.sleep to get the app to run on just one thread (the adobe api
can't handle multiple threads).  This works, but causes the service to show
as starting (not started) in the service viewer area of CompManagement in the
MMC.  I'm not worried about this.

Code for OnStart...
       Dim i As Integer = 5000 'Length of time to sleep the thread while
waiting for the next thing to come along...
       Dim f As FileInfo
       Dim d As New DirectoryInfo("c:\Pdf Populator Service\InBox")

       Do Until blnStop = True
           For Each f In d.GetFiles()
               If f.Extension = ".xml" Then
                   Timer_KillAdobeWindow.Start()
                   MakeCallToProcessFiles()
                   FinishProcessing(True)
                   Timer_KillAdobeWindow.Stop()
               End If
           Next
           Thread.Sleep(i)
       Loop

As long as all the parameters for the text boxes in the PDF meet the PDF
requirements, the program will populate the PDF, save it and email it out (or
fax it).  The problem comes if bad data is passed to the program and Adobe
will not accept it (example: a date value with 2 digit year).  When this
occurs when the app is running as a windows form a MessageBox is thrown from
Adobe.  I use my WindowsCloser Class on a timer to enumerate open windows
looking for such a window and send an enter key to the window using
System.Windows.Forms.SendKeys.  On the Windows Forms version this works, but
with the Windows Service version of the app, things keep hanging up.  I try
to attach to the process to debug, but don't seem to get anything (perhaps
because the program is waiting on a return from Adobe?).  Sometimes, using
taskmanager to endprocess on the Adobe app will suddenly throw an exception
in the .Net Service App.

For the timer, I'm using
Friend WithEvents Timer_KillAdobeWindow As System.Timers.Timer

My Windows Closer Class called from the elapsed event on the async timer is
...
Option Explicit On
Option Strict Off

Imports System
Imports System.IO
Imports System.Text
Imports System.Runtime.InteropServices
Imports System.Threading

Public Delegate Function CallBack(ByVal handle As Integer, ByVal param As
IntPtr) As Boolean

Public Class LibWrap
   ' Passes a managed object instead of an LPARAM.
   ' Declares a managed prototype for the unmanaged function.
   Declare Function EnumWindows Lib "user32.dll" ( _
      ByVal cb As CallBack, ByVal param As IntPtr) As Boolean
End Class 'LibWrap

Public Class WindowCloser
   Shared cstrPartialTitle As String

   Public Shared Sub GetWindowFromTitle()
       Dim tw As TextWriter = System.Console.Out
       Dim gch As GCHandle = GCHandle.Alloc(tw)
       ' Platform invoke prevents the delegate from being garbage collected
       ' before the call ends.
       Dim cewp As CallBack
       cewp = AddressOf WindowCloser.CaptureEnumWindowsProc
       LibWrap.EnumWindows(cewp, GCHandle.op_Explicit(gch))
       gch.Free()
   End Sub 'GetWindowFromTitle
   Public Shared Function CaptureEnumWindowsProc(ByVal handle _
         As Integer, ByVal param As IntPtr) As Boolean
       Try
           Dim gch As GCHandle = GCHandle.op_Explicit(param)
           'Dim tw As TextWriter = CType(gch.Target, TextWriter)
           Dim w As New Window
           Try
               w.h = handle
               If w.GetText = PartialTitle Then
                   AppActivate(PartialTitle)
                   System.Windows.Forms.SendKeys.Send("{Enter}")
               End If
               Return True
           Catch ex As Exception
               'do nothing
           Finally
               gch = Nothing
               w = Nothing
           End Try
       Catch ex As Exception
           'do nothing
       End Try
   End Function 'CaptureEnumWindowsProc
   Public Shared Property PartialTitle() As String
       Get
           PartialTitle = cstrPartialTitle
       End Get
       Set(ByVal Value As String)
           cstrPartialTitle = Value
       End Set
   End Property
End Class
Public Class Win32API
   Public Declare Auto Sub GetWindowText Lib "User32.Dll" _
   (ByVal h As Integer, ByVal s As StringBuilder, ByVal nMaxCount As Integer)
End Class
Public Class Window
   Friend h As Integer ' Friend handle to Window.
   Public Function GetText() As String
       Dim sb As New StringBuilder(256)
       Win32API.GetWindowText(h, sb, sb.Capacity + 1)
       Return sb.ToString()
   End Function
End Class