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The issue occurs because your MS-Office 2007 version by default doesn't have the support of ExportToPDF, you need to download and install the support from the Microsoft website.
Steps to download:
1. 1. Click on the below URL.
2. Download the file by clicking the Download button and saving the file to your hard disk.
3. Double-click the SaveAsPDFandXPS.exe program file on your hard disk to start the Setup program.
4. Follow the instructions on the screen to complete the installation.
5. After you install this download open the document you want to publish and then, depending on the program you are using, select Save or Publish to PDF or XPS from the Office or File menu.
(Referral URL : https://www.microsoft.com/en-in/download/details.aspx?id=7)
Please, do contact us if you have additional queries. Thanks again!