The ability to add notes to a selection for PDF files exists for some time in Canary builds of Microsoft Edge. However, only today the company officially announced it, and shared some details on how it works.
If you select some text in a PDF file, you can right-click on the selection and add a comment to it. The sticky note-like user interface will allow you to express some idea regarding the selection you want to remember.
Here's how it looks:
When you click on the Add comment entry, it will open the following dialog:
There, you can type some note, and it will be attached to the selection once you click on the check mark icon.
The selection will become highlighted. You can open the attached note by right-clicking on the highlight and then selecting Open comment from the context menu.
Microsoft notes the following regarding this new addition.
The ability to add text comments on PDF documents is one of the features we provided for the PDF reader in legacy Microsoft Edge.We have heard feedback that some of you miss this useful feature,so we are pleased to announce that we are bringing it back to Microsoft Edge!Here is how you can access this functionality in the latest version of Canary and Dev.
Once you are done adding your comments on the document, you can save the document so that your comments are saved as part of the document. You can access the comments anytime later by opening the saved document in Microsoft Edge.
Microsoft encourages Insiders to leave their feedback about the PDF notes feature.