Form fields are unavailable after sending by email

I open PDF file with fillable form fields, fill some of them, then send the file to someone else to fill the rest of them. This represents scenario where Human Resources pre-fill the form for an employee, and he has to fill the rest, sign and return.

If I'm sending the document using Adobe Reader's email feature, when the recipient opens up the file he received from me, there are no longer any fillable form fields, so he can't fill them.

This happens only when I'm using Reade's feature to send document by email (using default mail application/Outlook). If I save the file with partially-fllled fields and then attach it to the email like any other file, then it remains intact, and form fields remain available to the recipient.

I wonder if this is by design, or perhaps something can be changed in Preferences, so the recipient can continue with form fields even if I sent the file from within Reader.