Can I highlight and annotate PDFs with Zotero?
Zotero will open PDFs with your computer's default PDF viewer. You can annotate PDFs with a variety of programs, including Adobe Reader/Professional, FoxIt, Nuance PowerPDF, PDF-XChange, macOS Preview, Microsoft Reader. So long as the program saves the annotations to the PDF file, the annotations will sync with zotero.org and your other devices.