Using External PDF Editors

PDFs are more complex than they look. Under the hood, they're a spaghetti-like network of things such as XObjects, Arrays, Page Tree Nodes, and Optional Content Groups. That's why some edits can't be undone in Acrobat (Figure 14.24). You'd break the spaghetti.

Figure 14.24. There is no Undo command for many operations in Acrobat. This is nature's way of letting you know that PDF files are more complicated than you might think. At least you're warned.

Even if you're using some of the excellent, third-party add-ons for Acrobat to perform edits, it's advisable to work on a copy of your file just in case things fall apart.

As for using Adobe Illustrator to edit PDF files...don't. We've all done it in desperation in the olden days before PitStop and other PDF-editing software. There was no viable alternative back then, and deadlines will drive you to do such things. But if it wasn't generated by Illustrator, opening a PDF file in Illustrator without the necessary fonts available will wreck font embedding, and manipulating objects may cause unexpected loss of content. It's OK to edit PDFs saved directly from Illustrator, however. They're special files: The original Illustrator file is contained within the PDF, and that's what you'd actually be editing, provided you use the default option to retain Illustrator editing capabilities. But you're risking the possibility of file damage when you use Illustrator to edit PDF files created by other applications. It's preferable to return to the originating application to make edits. Then create a new PDF file and go on with your life.