Hello Rerock,

This macro will search all open PDF documents. If the given document is found then it is closed.

The document name matching is not case sensitive. You may use either the full document name or part of the name to match an open document.

Copy this code into a VBA Module in your workbook.

Macor Code to Close an Opened PDF File
' Written:  October 08, 2014
' Author:   Leith Ross
' Summary:  Searches all open PDF documents. If a document is found that matches the
'           given file name either fully or partially, it will be closed. If the given
'           file name is not found to be open then a dialog message alerts the user.


' 32 Bit Windows API calls.
Private Declare Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
         
Private Declare Function GetWindowText Lib "user32.dll" Alias "GetWindowTextA" (ByVal hWnd As Long, ByVal lpString As String, ByVal aint As Long) As Long
          
Private Declare Function GetWindow Lib "user32.dll" (ByVal hWnd As Long, ByVal wCmd As Long) As Long

Private Declare Function GetClassName Lib "user32.dll" Alias "GetClassNameA" (ByVal hWnd As Long, ByVal lpClassName As String, ByVal nMaxCount As Long) As Long
        
Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Sub ClosePDF(ByVal FileName As String)

    Dim Found   As Boolean
    Dim hWnd    As Long
    Dim Pid     As Long
    Dim RefCell As Range
    Dim ret     As Long
    Dim Title   As String
    Dim Tid     As Long
    Dim WndCls  As String
    
    Const GW_HWNDNEXT   As Long = 2
    Const WM_CLOSE      As Long = 16
    
       If FileName = "" Then Exit Sub
       
        hWnd = FindWindow(vbNullString, vbNullString)

        Do Until hWnd = 0
            WndCls = String(512, Chr(0))
            ret = GetClassName(hWnd, WndCls, 512)
                If Left(WndCls, ret) = "AcrobatSDIWindow" Then
                    Title = String(512, Chr(0))
                    ret = GetWindowText(hWnd, Title, Len(Title))
                    If InStr(1, Title, FileName, vbTextCompare) Then
                        ret = SendMessage(hWnd, WM_CLOSE, 0, ByVal 0)
                        Found = True
                        Exit Do
                    End If
                End If
            hWnd = GetWindow(hWnd, GW_HWNDNEXT)
        Loop
  
        If Not Found Then MsgBox "The Following PDF Document Was Not Found :" & vbCrLf & vbCrLf & FileName
        
End Sub
Example of Using the Macro
Sub CloseTest()

    ClosePDF "Signed Agreement"
    
End Sub