Unfortunately, Publisher doesn't have a viewer for opening and viewing Publisher (.pub) files. But if you want to send a publication or receive a publication in email, you have some options.
Sending a publication
If you send publications to people who don't have Publisher installed on their computers, you can try:
Converting the publication to a PDF file, and sending it as an attachment in email.
Posting the publication to a website and sending a link to readers.
Converting the publication to email so it appears in the body of an email message.
Receiving a publication
If you receive a Publisher (.pub) file in email and you can't open it, you can download the latest Office trial that includes Publisher 2013.
Using the trial version, you can also learn more about how Publisher can help you create professional-looking publications.
After the trial expires, you can still use the trial version as a viewer for Publisher files, even though you can no longer create or change publications.