A family of Microsoft word processing software products for creating web, email, and print documents.
Joe is correct, the feature is annoying.
The problem occurs in some Emails and a form to fill in in Word.
The behavior in e-mails isn't controlled by Word. Check the settings of your e-mail program.
If by "form" you mean a protected form with text form fields, then you are quite right: selecting part of the text in a field is tricky.