Open a PDF file using the 'CreateFileMoniker' API in VB.NET

[IT_Researcher]

I am looking for ways to open a PDF document using the 'CreateFileMoniker' API call. I have observed using certain API monitoring tools that when we have a file path (such as a PDF) in a Microsoft Excel document mentioned as a hyperlink, the click action calls the 'CreateFileMoniker' which makes many other calls and finally opens the PDF file.

I have not seen Process.Start or ShellExecute being present directly in those calls and I would like to replicate the same for one of my application using a VB.NET code. This is the code I have, but it throws a Failed. HRESULT=800401EA error message. Took help from ChatGPT and other sources but to no avail.

Imports System.Runtime.InteropServices
Imports System.Runtime.InteropServices.ComTypes

Public Class Form1

    <DllImport("ole32.dll", CharSet:=CharSet.Unicode)>
    Private Shared Function CreateFileMoniker(
        ByVal lpszPathName As String,
        ByRef ppmk As IMoniker
    ) As Integer
    End Function

    <DllImport("ole32.dll", CharSet:=CharSet.Unicode, PreserveSig:=True)>
    Private Shared Function CoGetObject(
    ByVal pszName As String,
    ByVal pBindOptions As IntPtr,
    <[In]()> ByRef riid As Guid,
    <Out(), MarshalAs(UnmanagedType.Interface)> ByRef ppv As Object
) As Integer
    End Function

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        '  Dim pdfPath As String = "C:\temp\file.pdf" 
        ' Create the IUnknown GUID
        Dim IID_IUnknown As New Guid("00000000-0000-0000-C000-000000000046")

        Dim unk As Object = Nothing
        Dim hr As Integer = CoGetObject("file://" & pdfPath, IntPtr.Zero, IID_IUnknown, unk)

        If hr = 0 AndAlso unk IsNot Nothing Then
            MessageBox.Show("PDF opened successfully via OLE/COM.")
        Else
            MessageBox.Show("Failed. HRESULT=" & hr.ToString("X"))
        End If
    End Sub

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

    End Sub

The API sequence ( not exhaustive ) drafted by observing the process used by MS Excel to open the PDF hyperlink file is as below:

1.When PDF file is opened from hyperlink through excel, the HLINK.dll calls the API "CreateFileMoniker"

2.The KERNELBASE.dll calls the API wcschr

3.urlmon.dll calls the API wcschr

4.Finally, the HLINK.dll calls the "GetFileAttributesW" API

5.This then inititates "RtlDosPathNameToNtPathName_U_WithStatus"

6.Acrobat reader comes into picture

7.Call to "RtlDosPathNameToRelativeNtPathName_U_WithStatus"

Which then initiates "ExtTextOutW''

How to modify my code to achieve the same in VB. NET?

The method tried is mentioned above

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EDIT 09-09-2025

The actual purpose of our question is to look for a best method to open a file using it's default application in Windows using VB.NET application. We are presently using ShellExecute, but the process gets interfered by Antivirus software present in the PC. When tried by pasting it as a file link into a cell of MS Excel, and opened using Hyperlink, there was no antivirus interference. We posted about CreateFileMoniker as we observed this during the API calls as stated above. Any other such foolproof method to avoid AV interference is also ok

************

[Niya]

You know this isn't VB6, where you have to resort to this kind of arcane wizardry to do simple things like opening a PDF. I am 100% certain you can very easily find a dozen Nuget packages that deal with PDFs.

[IT_Researcher]

@Niya Please check today's EDIT in the question for our actual requirement.

[Niya]

There is no COM class to represent a PDF as far as I know so Monikers won't work here.

[IT_Researcher]

@Niya . Sure, but could you please suggest us which of the following methods are preferable to open any file programmatically using VB .NET, and which has less chances of getting interferred by Antivirus software or Security software ? 'Process.Start with UseShellExecute as True' v/s ShellExecute . Or if any better method that is also fine.

[Niya]

Ok, but first, let's be very clear about what you are looking for. Do you want to open and display the entire PDF? Do you want to write to it, or do you want to extract something specific from the PDF, like an image or piece of text?

[Niya]

In the meantime you can try the "open" verb which may be less suspicious to AVs:-

        Dim pi As New ProcessStartInfo

        pi.Verb = "open"
        pi.FileName = "c:\temp temp\test.pdf"
        pi.UseShellExecute = True

        Process.Start(pi)

[IT_Researcher]

I want to open PDF, Excel, and Word (.docx) files with their default programs fully, just like if the user double-clicked them. I do not want to make them read-only or hide any part of the file.

[IT_Researcher]

Ok, but first, let's be very clear about what you are looking for. Do you want to open and display the entire PDF? Do you want to write to it, or do you want to extract something specific from the PDF, like an image or piece of text?

I want to open PDF, Excel, and Word (.docx) files with their default programs fully, just like if the user double-clicked them. I do not want to make them read-only or hide any part of the file.

[PlausiblyDamp]

You should be able to do this directly with the Process object. something like the following should do the trick (not tested however)

Dim myProcess As New Process
myProcess.StartInfo.FileName = "<path to the file you want to open>"
myProcess.StartInfo.UseShellExecute = True
myProcess.StartInfo.RedirectStandardOutput = False
myProcess.Start()
myProcess.Dispose()