There are 3 factors affecting the author name for newly added annotations:
1: The author name that you have changed for an existing comment and set it as default.
2: The first name and last name that you have set in your Foxit account profile.
3:The settings under File> Preferences> Identity in Foxit Reader.
The priority order is 1>2>3
Following are the specific process:
1):No matter whether you have logged in Foxit account in Foxit Reader or not , please choose to change author name for an existing comment in your PDF file by right clicking on the a comment >Choose ..option in the pop-up context menu,set a new Author name under the Generaltab in the pop-up comment properties dialog box, then hit Set current properties as default ，click Close.
After you set the new author name and set it as default in an existing comment,then same sort of comments you add again will automatically use the author name that you have set.
Note:The modified author name will only be applied to newly added annotations of the same type. For example,you change author name and set it as default for an existing typewriter annotation,then modified name will only be applied to newly added typewriter annotations,it won't be applied to other types of annotations（For example, Textbox annotation）.
2):Click on the people icon on the top right corner in Foxit Reader to login in with your Foxit account and password. After you having logged into Foxit account in Foxit Reader,please double click on the people icon again to bring up a My Account window where you could set First Name and Last Name there.
And go to File >Preferences>Commenting>check option Always use user name of the log-in account for author name and click OK.
Then all of your newly added annotations will show author name as “acount's First Name+account's Last Name". Even if you don't set First Name and Last Name for your Foxit account, the newly added annotations will show author name as "That part of the email contents before the @ sign".
For example,I have logged into Lisa_li@test.com this account in Foxit Reader without setting Firt Name and Last Name in Foxit account,then the newly annotations in PDF file will have Lisa_li as their author name.
3):Don't log into Foxit account in Foxit Reader,then go to File>Preferences>Identify,set First Nameand Last Name under Identify,click OK.
Then all of your newly added comments will show author name as the "Identify's First Name in preferences+Identify's Last Name in preferences".
If you don't have set First Name and Last Name under Identily in Preferences, then newly added comments will show author name as "Login name" that you could see under "File>Preferences>Identify".