PDFill has the most complete functions In the free pdf editing software
Combine multiple pdf files, convert images to pdf files, rearrange files, add watermarks, encrypt, decrypt, etc.
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PDF-XChange Viewer - A PDF Reader that replaces Adobe Reader
PDF-XChange Viewer (PDF-XChange Lite Free) - PDF reading and annotation tool, which can add annotations, text, lines, lines, graphics, stamps on the PDF, and the best PDF to image function (File → Export), multi-page browsing mode, let you switch more easily when opening multiple files.