As of Xodo version 4.5.27, you can create Sound Annotations or sound notes in your PDF document. Please note that this feature will need microphone permission on your Android device in order to record sound. Here's a short guide on how:
1. Go to the Insert section and select the Sound Tool for Sound
2. Tap on an empty space in your document to start recording.
Please note that this feature will need microphone permission on your Android device in order to record sound, and a dialog asking for this permission will appear the first time you use this feature. When you're done, tap Stop:
3. You can then preview your recording, record a new audio file, or finish the recording session:
4. When you're all finished, you'll see your Sound Annotation in your document and you can tap on it to listen to it or modify it: