Unfortunately there is almost no way by which the recipient of a Microsoft Publisher file can open it without the application, either to view or convert.
There are several things that the sender of the file can do however to enable the recipient to view the document.
First of all, the sender can avoid saving documents as .pub files. This is the default option for Microsoft Publisher, but of course prevents anyone not using Publisher from opening the saved document.

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By using the
Save As... option and choosing an alternative option on the
Save as type drop down will enable the sender to select a popular save option.
Alternative file types to save a Publisher .pub file include:
These 4 options will retain (or provide an accurate representation of) the original formatting of your Publisher document.