VBA to convert multiple PowerPoint files into one pdf

Hello,

From an excel workbook, I want to select a folder (with filepath referenced in cell k3) containing approx 20 PowerPoint presentations and export their content into a pdf file with the same name as the original but with the new .pdf suffix. I found some vba online which I have tried to adapt but it gives an error on the line which is removing the file extensions. Please would someone be willing to take a look and advise?

This is the line which is currently giving the error but I don�t know if this is the only problem;

removeFileExt = InStr(1, oPPTFile.Name, ".") - 1

Thank you,

Jess

Sub ppt2pdf()
Dim oPPTApp As PowerPoint.Application
Dim oPPTFile As PowerPoint.Presentation
Dim onlyFileName As String, folderpath As String, pptFiles As String, removeFileExt As Long
 
Application.ScreenUpdating = False
 
'initialize variables
folderpath = Range("k3").Text & "\"
'pptFiles = Dir(folderpath & "*.pp*") (Original)
pptFiles = (folderpath & "*.pp*")
 
'check for ppt files and exit if not found
If pptFiles = "" Then
    MsgBox "No files found"
    Exit Sub
End If
 
Do While pptFiles <> ""
 
'Assign powerpoint application to variable
Set oPPTApp = CreateObject("PowerPoint.Application")
oPPTApp.Visible = msoTrue
 
On Error Resume Next
 
'Assign powerpoint presentation to variable
Set oPPTFile = oPPTApp.Presentations.Open(folderpath & pptFiles)
 
On Error GoTo 0
 
'remove file extension and assign an only file name to a variable
removeFileExt = InStr(1, oPPTFile.Name, ".") - 1
 
onlyFileName = Left(oPPTFile.Name, removeFileExt)
 
On Error Resume Next
 
'Save ppt file to pdf file
oPPTFile.ExportAsFixedFormat oPPTFile.Path & "\" & onlyFileName & ".pdf", ppFixedFormatTypePDF, ppFixedFormatIntentPrint
oPPTFile.Close
 
'iterate to the next file in the folder
pptFiles = Dir()
Loop
 
'Close PPT application
oPPTApp.Quit
Set oPPTFile = Nothing
Set oPPTApp = Nothing
 
Application.ScreenUpdating = True
 
End Sub