So you want to modify the text of a PDF by hand (2020)
The PDF specification is wild. My current favourite trivia is that it supports all of Photoshop's layer blend modes for rendering overlapping elements.[1] My second-favourite is that it supports appended content that modifies earlier content, so one should always look for forensic evidence in all distinct versions represented in a given file.[2]It's also a fun example of the futility of DRM. The spec includes password-based encryption, and allows for different "owner" and "user" passwords. There's a bitfield with options for things like "prevent printing", "prevent copying text", and so forth,[3] but because reading the document necessarily involves decrypting it, one can use the "user" password to open an encrypted PDF in a non-compliant tool,[4] then save the unencrypted version to get an editable equivalent.[1] "More than just transparency" section of https://blog.adobe.com/en/publish/2022/01/31/20-years-of-tra...[2] https://blog.didierstevens.com/2008/05/07/solving-a-little-p...[3] Page 61 of https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandard...[4] For example, a script that uses the pypdf library.