Hi Mum,
This is the free 'PDF Merger and Splitter' app that saved me some time in the past, it works on Windows 10 and Windows 11: 

Guide:
 1. Click the link to open the app page - https://apps.microsoft.com/store/detail/pdf-merger-splitter/9P4TCNS9H432
 
 2. Click the 'Get in Store App' blue button on the right hand side. There may be a popup that says, do you want to open Microsoft store, you should click yes/continue.
 
 3. If it does nothing after clicking the blue button mentioned, its likely the app isn't supported on that computer. However it says 'Install' then its likely the rest of this will work, don't click install just yet.
 
 4. Ask the office if its okay to add the free 'PDF Merger and Splitter' App from the Microsoft Store. 
 
 5. If they agree (I hope, it would save some time), then click install, it will take a few minutes.
 
 6. Once you open the app, make sure to pin it to the taskbar so you can easily access it, do this by right clicking the app at the bottom of the screen in the taskbar and selecting 'Pin to taskbar'
 
 7. App usage is hopefully self explanatory..... Click merge..... add PDFs..... Merge PDFs. 

Hope that helps,
Ray