Share the technical implementation of Markdown export and publish copy in CodeWF.Markdown and Vex: MarkdownDocumentExporter, ExportKind, shared image loading, SVG/GIF/WebP rasterization, Word embedded media resources, selectable text PDF, Windows CF_HTML rich HTML clipboard, and extensible typography themes.
检查 PDF 文件中是否存在签名相关结构标记，辅助判断文件是否可能带签名。