Which version of Acrobat have you used to Reader Extend the form?
Ensure that you have selected the commenting option while reader extending the document , You can check this by clicking Ctrl + D when the form is opened using Reader and check the Document Restrictions Summary and check if commenting is allowed or not.
I posted the same question here:
and you can see what I was answered. However, I am not sure that answer is complete!
I am using Acrobat X ver. 10.1.7.
I checked what you suggested and commenting is not allowed. However I don't see how I can enable it.
In Acrobat X, I have the following 3 options:
1) File > Save As > Reader Extended PDF > Enable Adding Text In Documents
2) File > Save As > Reader Extended PDF > Enable Commenting and Measuring
3) File > Save As > Reader Extended PDF > Enable Additional Features
I am using the last one which should enclose the first 2 too.
As a user case, let me describe my situation: I have a submit button (mailto:"email_address") on the LiveCycle form. If I don't extend Reader rights by means of Acrobat option 3 said above, the submit button is not effective in Reader. However, if I process the file in Acrobat and choose option 3, the submit button works fine in Reader. That means that some extension has been done. However, commenting is always disabled. Here, the answer I got from the forum linked above may apply. Please, let me know your comments and opinions.
Thanks for your attention.
Okay , the option to reader extend the file you have chosen is correct but your form is dynamic XFA - Acrobat/Reader does not have capability to add annotations on dynamic XFA based PDF files hence you are not seeing that option.
If your usecase is to use annotations on the PDF then you can go with static forms (if possible)