Can you clarify what you meant by "web form"?
Is it a PDF that is shared for download through a web page/web server? Or is it an actual HTML form that needs to be exported to a PDF directly from the website that the users are hitting via web browser?
I am asking this because not all users have Adobe Acrobat Pro or Adobe Acrobat Reader.
And to avoid issues when such users try to sign your PDFs using a web browser, I would suggest that it may be better to employ Adobe Sign in this type of workflow.