How can I send a editable pdf via email?

++ Adding on to Gary's answer.

It is correct that you cannot edit a pdf file with a reader or the other person you are sending it to. You both need a paid version to edit the pdf file.

The max you can do with Reader is share the file.

You can send PDF files directly from Acrobat or Acrobat Reader using a webmail account like Gmail or Yahoo. To do so, you must add a webmail account in Acrobat and allow access to the account while signing in from Acrobat for the first time. 

How to share file, checkout this helpful article: https://helpx.adobe.com/acrobat/using/send-pdf-by-email.html 

Thanks,

Akanchha

You need Acrobat Pro (on the Mac) or Acrobat Standard or Pro (on the PC) to edit a PDF. If you have Acrobat Reader, you cannot edit a PDF. There's nothing you can do in Reader to make it easier or harder for the recipient to let them edit.

Just send them the PDF; that's about all you can do.