I want to tweak and then re-sign the RDP file downloaded from https://rds.example.com/rdweb the RD Gateway RD Web server to stop it being tampered with

Steps

With a browser on you local computer (I'm using Windows 11)

connect to https://rds.example.com/rdweb authenticate and then download the RDP file

For this example I will call the RDP file downloaded from the RDWeb server cpub-MyCollection-New-MyCollection-New-CmsRdsh.rdp

Open the cpub-Desktop-New-Desktop-New-CmsRdsh.rdp file in notepad and remove both the following configuration keys and their values (for signatures:s: it's a big block of certificate text)

signscope:s:
signature:s:

Make any edits you want to make either by editing the RDP file open in notepad, or right clicking on the RDP file and selecting More options and the Edit on the context menu

On the RD Gateway or RD Web Server

Export your rds.example.com certificate and private key from your RD Gateway / RDWeb server. Provide a password and copy it to your local machine e.g. as rds.example.com.pfx (file name is not important)

On your local computer

Right click on the exported pfx file choose Install pfx from the context menu

In the Welcome to the Certificate Import Wizard select:

Current User

Browse to the pfx file

Enter the password, mark the key as exportable at the Private key protection dialog

Choose Automatically select the certificate store

The certificate should be in Certificates - Current User => Personal => Certificates in the "Manage user certificates" or to open it via command line user certmgr.msc

Open the certificate by double clicking it and then select the details tab scroll and copy the thumb print

Open a terminal and then run rdpsign

rdpsign /sha256 5f70f96a2d9737f332d3043f205645a40e1b5397 "C:\temp\cpub-Desktop-New-Desktop-New-CmsRdsh.rdp"
All rdp file(s) have been succesfully signed.

Distribute your signed RDP file to your users.

Possible error when you don't have the cert available

Unable locate the certificate specified.  Error Code: 0x80092004
The rdp file could not be signed.  Error Code: 0x80092004

If you have the path to the rdp file wrong rdpsign will throw:

Unable to use the certificate specified for signing.  Error Code: 0x80070490
The rdp file could not be signed.  Error Code: 0x80070490