When you need to add comments into a PDF using Adobe Acrobat Reader there is a workaround that allows you to change the author name that will be included in each comment.
1. Open the PDF and Add sticky note (Ctrl + 6)
2. In the sticky note box, right click next to the author name and then select Properties...
3. Now you can edit the Author name in the General tab. Make sure to check the box for "Make Properties Default". Click OK.
4. Now all new comments will have the new author name. All previous comments made before changing the author name will remain the same.
NOTE!
There is one setting in Adobe Acrobat Reader to be aware of. If, for instance, you DO want to use your Windows login ID for commenting, you can choose to do that at any time. In Edit > Preferences (Ctrl + K), in the Commenting page, there is a checkbox for using your Log-in name. Check the box and all comments will have your Log-in name as default author name.
Also note that when you do wish you use something else than your Log-in name, make sure the checkbox is NOT ticked and then follow the procedure above to edit the author name that will appear in future comments.