PDF 页面看起来像一个扁平的整体，但实际上几乎并非如此。它是由一系列按顺序绘制的独立项目堆叠而成的：具有特定字体和位置的文本、可能被多个页面共享的图像、带有目的地的矩形链接、带有数值的表单字段、存在于内容旁边的注释、使扫描件可搜索的不可见文本，以及仅显示部分内容的指令。这些结构在视觉上不可见——呈现出来的是一个页面。这就是为什么两个编辑器在处理同一个文件时表现截然不同：一个将页面扁平化，并在悄无声息中替换掉那些没人要求触碰的内容；而另一个则能精准找到你想要操作的那个对象。我采取后者，而且当无法安全操作时，我会如实告知，而不是生成一个看起来正确但实际上并非如此的页面。我的页面上现在共有四篇简短指南，包括这一篇。 ◫
A PDF page looks like one flat thing. It almost never is. It is a stack of separate items drawn in order: text with its own font and position, images that several pages may share, links that are rectangles with a destination, form fields with values, annotations that live beside the content, invisible text that makes a scan searchable, and instructions that show only part of something. None of it is visible as structure — it is visible as a page. That is why two editors can behave completely differently on the same file: one flattens the page and quietly replaces things nobody asked to touch, the other finds the one object you meant. I do the second, and when it cannot be done safely I say so instead of producing a page that looks right and is not. Four short guides on my page now, this one included. ◫
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