When you open a publication (*.pub) in Publisher you may get the following message: “Publisher had detected a problem in the file you are trying to open. If you are certain that this file came from a trusted source and does not contain harmful information, click OK. If you received this file from another person or machine and are not sure that the contents are safe, click Cancel.” CTRL+SHIFT+I turns on the alert ID (1100818)
If you click the OK button on the message you get the error: “Publisher cannot open the file.”
What this tells me is that the file is probably corrupt or not a supported Publisher file (either super-old version of Publisher no longer supported or just not a real publisher file, like someone renamed a file extension to pub from something else somehow).
The bad news is the file may destroyed beyond recognition. The good news is you may be able to salvage some of the content from it. To do this, try to insert the file into a new publication using the Insert/Text File command (in Publisher 2010 it’s now called Insert File under the Insert tab.
Create a new publication and go Insert/Text File…, then browse to the corrupt publication (*.pub) file, select it and click OK.