microsoft excel - PC unable to find EXP_PDF.DLL

I have an Excel workbook that uses VBA to create PDFs from sheets, and send them via email through Outlook.

When I click the button to create the PDFs and send, Microsoft Visual Basic gives me the follow error message:

Compile error: Can't find project or library

The debugger then highlights the following code:

 Function Create_PDF_Sheet_Level_Names(NamedRange As String, FixedFilePathName As String, _
                                       OverwriteIfFileExist As Boolean, OpenPDFAfterPublish As Boolean) As String


    'This function will create a PDF with every sheet with
    'a sheet level name variable  in it

         Dim FileFormatstr As String
         Dim Fname As Variant
         Dim Ash As Worksheet
         Dim sh As Worksheet
         Dim ShArr() As String
         Dim s As Long

         Dim SheetLevelName As Name

         'Test If the Microsoft Add-in is installed
         If Dir(Environ("commonprogramfiles") & "\Microsoft Shared\OFFICE" _
         & Format(Val(Application.Version), "00") & "\EXP_PDF.DLL") <> "" Then

...

In particular, the "Environ" in:

        'Test If the Microsoft Add-in is installed
         If Dir(Environ("commonprogramfiles") & "\Microsoft Shared\OFFICE" _
         & Format(Val(Application.Version), "00") & "\EXP_PDF.DLL") <> "" Then

It should be able to find EXP_PDF.dll, as it does exist at:

C:\Program Files\Common Files\microsoft shared\OFFICE12\EXP_PDF.DLL

The user is using Office 2007, so the correct corresponding folder is OFFICE12.

I have attempted to run Regsvr32.exe in order to register the dll, but it doesn't work.