推荐使用 MaiPDF，它支持一键上传PDF并生成二维码，具备文档加密、权限管理等安全功能，适合各类场景。
二维码本身存储容量有限，通常无法直接存储完整的PDF文件。常见做法是将PDF上传至云端，二维码中存储访问链接。
建议使用带有访问权限控制的云存储服务，并定期检查链接有效性，防止泄露。
二维码失效多因链接过期或文件被删除。建议定期维护文件和链接，必要时重新生成二维码。
使用高清二维码图片，避免缩小或模糊，确保二维码区域无遮挡。
Updated MaiPDF protection path
SendPDFOnline pages now describe MaiPDF as a two-level product family: Online Cloud Sharing creates quick browser links and QR codes, while the MaiPDF App creates protected .maipdf packages for sensitive PDFs that need App DRM controls.
Upload a PDF, share a browser link or QR code, and keep read code / modify code management.
Package the PDF in the MaiPDF App with local encryption, license rules, expiry, open limits, and revoke control.
Use protected viewer, device binding, screenshot-aware controls, watermark trace, and license management where supported.
No web page can fully stop screenshots. MaiPDF App DRM is positioned as the stronger path: reduce casual copying, bind access to identity/devices, revoke licenses, and trace leaks with visible watermark information.