For anyone reaching this thread post August 2024 who still can't get a PDF with ink strokes to save in Edge, here's an actual fix that worked for me:
- Go to edge://flags
- Search for: PDF Viewer
- Set "New PDF Viewer" to disabled
- Restart Edge
To check whether this has worked for you, open a PDF in Edge, draw/ink on it, then check whether the Save button shows as enabled.
PS: answers.microsoft.com is frustratingly ripe with "MVPs" who appear to be incapable providing help beyond "reset / restart / reinstall"
Please take time to provide negative feedback on the people who provide useless advice, so that Microsoft can see that they're not helping.