This is not something you can do manually since PowerPoint do not facilitate you with such options like saving the output file into PDF format. Therefore only option left in order to accomplish this task is to make use third party repair tool. Now there are several tools available that claims to be useful including paid tools and freeware also.
But I would recommend you to go for PPT to PDF converter. PPT to PDF converter is trendy converter that permits users to transform PPT projects into PDF file with superior quality and no loss of data. This tool is also capable of performing Batch conversion. With this you can convert PPT, PPTX, PPTM to high quality of PDF file, without losing the quality of your PPT file content like text, tables, image, layout etc.http://www.softwaredownloadcentre.com/software/powerpoint-to-pdf.php