Please be advised that the following was written or last updated a while ago and may therefore contain outdated information or opinions I no longer hold. 请知悉下文自写作或上次更新已届相当时限，或包含过时信息及已摒弃观点。
PDF Viewer/PSPDFKit 开发商的博客蛮好的，虽然主要是在写自己产品用法，但是也有不少比较适合快速了解 PDF 格式