Microsoft Publisher files (.pub) can only be opened with Publisher. In the absence of Publisher, you can convert files to PDF. This will allow you to open the file in a variety of ways, including using a web browser. If you have Publisher, you can simply save the file as PDF.
Steps
Method 1 of 2: Convert Online (Without Using Publisher)

Step 1. Visit a website with an online converter
To convert a file from the PUB (Publisher) format to PDF, you can use the online service. Here is a list of the most popular online resources for doing this:
- Zamzar - zamzar.com/convert/pub-to-pdf/
- Online2PDF - online2pdf.com/pub-to-pdf
- PDFConvertOnline - pdfconvertonline.com/pub-to-pdf-online.html

Step 2. Upload the PUB file you want to convert
Click the "Choose Files …" or "Select File" button. Find the PUB file you want to convert on your PC. The file upload process may take several minutes.

Step 3. Select the target format (if necessary)
On some sites, you will have to manually select "PDF" as the output format to save. In all other cases, "PDF" will be installed by default.

Step 4. Click “Convert” to start the conversion process
Your file will be sent to the site for further processing. The process itself takes place on the servers of the online resource.

Step 5. Download the converted file
At the end of the process, you will be provided with a link to download the resulting PDF to your computer. Download the PDF and open it with any PDF reader. You can also use a web browser for this purpose.
Zamzar will send the download link to your inbox
Method 2 of 2: Converting using Publisher

Step 1. Open the PUB file in Publisher 2007 or later
Earlier versions of Publisher do not support saving as PDF. Use the instructions below to save as PDF using Publisher 2003 or earlier.

Step 2. Activate the File drop-down menu or click the Office Button and select Save As
You may be asked for a path to save the file.

Step 3. Click on the "File Type" drop-down menu and select "PDF (*.pdf)"
This will allow you to save the file in PDF format.
You may need to install the Microsoft extension for Publisher 2007 to do this

Step 4. Click on "Options" to optimize your document for PDF (if necessary)
Publisher allows you to optimize your document for PDF.
- The Publish Settings window allows you to adjust the image resolution.
- Click "Print Options …" to configure the print options for your document.

Step 5. Save the file
Select a location on your computer to save the file in PDF format. Now you can open the resulting PDF file with any program designed for this.