概述：PDF文件结构及解密相关工具
Blogs explaining the internals of PDF
- https://www.adobe.com/devnet/pdf/pdf_reference.html
- https://resources.infosecinstitute.com/pdf-file-format-basic-structure/
- https://planetpdf.com/navigating-the-internal-structure-of-a-pdf-document/
- https://blog.idrsolutions.com/2013/01/understanding-the-pdf-file-format-overview/
- https://web.archive.org/web/20141010035745/http://gnupdf.org/Introduction_to_PDF
- https://www.w3.org/WAI/WCAG20/Techniques/ua-notes/pdf
Tools
- PdfView - Peeking into the Internals of PDFs - View the structure of PDF
- xpdf - Extracting text etc..
- pdf2xml - Extracting structure etc..
- Dragon00007/DecryptPDF: Decrypt/Unlock pdf files