Sometimes candidates will convert their resume/CV to PDF format before sending it to a recruiter. This is typically because they don't want anyone to make changes to their resume, and believe that PDF is a "read-only" document. A PDF file CAN be edited with the correct software, so this is a false assumption by job seekers.
Furthermore, many of the free tools that convert Word (or other) document types are loaded with adware, spyware, or other malware, if not actual viruses. They often create PDFs that are corrupted or otherwise not good-quality conversions. We are seeing more and more of these types of corrupted PDF resumes in Marketplace.
The best format for a resume is a Word (or other) document, without embedded tables or images.
If your candidate insists on using a PDF, please suggest they use the built-in conversion tool that is included with Word, versions 2007 and newer. Here's a great article that provides good instructions on how to convert a Word doc to PDF.