I am upgrading to a Windows 7 64-bit Professional from a Windows 7 Home Premium (32-bit) environment. I have large files created with Publisher 2007, and am aware that Publisher 2007 will not function in the new environment. I have successfully installed and am using Office 2007 in the 64-bit machine. If I purchase Publisher 2013, will it co-exist with Office 2007, and will files created with 2007 be accepted by Publisher 2013?
In my experience, 32bit Office2007 works just fine on 64bit Windows7. But, I don't use Publisher myself, so I've not encountered the limitation you mention. (could you explain further the issue you experience, or provide a reference?)
Office2013 products, when purchased through Retail, are usually provided in Click2Run installer format, and this offers co-existence with other Office versions.
I did find these articles, which may be helpful:
Publisher 2010/2007 Compatibility Issue -- Problems Opening 2007 Documents in 2010
https://social.technet.microsoft.com/Forums/office/en-US/cd63bc8c-6867-46f9-8de9-cbc33f7d91a4/publisher-20102007-compatibility-issue-problems-opening-2007-documents-in-2010
Changes in Publisher 2010 (for IT pros)
https://technet.microsoft.com/en-us/library/ee694636(v=office.14).aspx
Users can open, edit, and save any Publisher 2003, Office Publisher 2007, Publisher 2010 32-bit edition, or Publisher 2010 64-bit edition file on a computer that is running either a 32-bit or 64-bit Windows operating system
Changes in Office 2013
https://technet.microsoft.com/en-us/library/cc178954(v=office.15).aspx
What's new in Publisher 2013
https://support.office.microsoft.com/en-au/article/Publisher-2013-8a665c00-8497-4f17-8e2a-8fca3da92683