Plus all the fun of the fact that you can embed the following formats inside a PDF: There’s always some utterly insane file that Acrobat opens just fine and now you get to play the game of figuring out how Acrobat repaired it. Acrobat tolerates unfathomably malformed PDF files generated by old software that predates the opening-up of the standard when people were reverse-engineering it. would be much better for humanityĭespite the thousands of pages of ISO 32000, the reality is that the format is not defined. I have had about 10% success with Preview.app detecting the lines and allowing me to click on them and type, but having. I am sure we ended up in this situation because people just "File > Print to PDF" from Word or whatever, because knowing that PDF forms exist and then how to use Adobe(R) whatever(tm) to make a real editable PDF is "too much to ask." My handwriting is terrible, and it's a waste of human capital for some poor soul to try and decipher handwriting only to (almost undoubtedly) re-type it into a computer on their end ) and replace those _ areas with actual PDF inputs. That has been on my wishlist for several years: build a "PDF annotation" service that takes in a PDF that is not an XObject form (e.g. > it's harder to take an existing, outdated, non-editable PDF and automatically fill it out. However, Googling for simple PDF files yielded this, which I feel is very readable in a text editor. To get a feel for it, following the official spec when reading a simple-looking document can help.Įdit: I didn't link any actually useful resources, in part because I actually just have a corpus of files in various file formats that I keep handy as a reference for some weird reason. The part you're most likely interested in is the content streams, which contain postscript-like drawing commands. Then, the xref table itself points to the latest version of all of the objects. The first thing that is read is actually an offset pointing back to the xref table, at the end of the file. One trick for getting started: PDFs are read from the bottom. If you open up a simple/old PDF in your favorite text editor, you can begin to grok the basic structures quite easy. It's actually not so bad: it's mostly ASCII, even though some parts of it really need to be treated as binary. It sounds like it might satisfy your use case. For PDF, it uses a dynamically instrumented version of the PDFminer parser. Shameless plug: I am one of the maintainers of PolyFile, which, among other things, can produce an interactive HTML hex editor with an annotated syntax tree for dozens of filetypes, including PDF. For example, with PDF, what if you have a PDF object stream that has a length that doesn't agree with the position of its `endstream` token? What if you have a PDF dictionary with duplicate keys? Do you use the value of the first key or the second? What if you have two, valid PDFs concatenated one after the other? Do you render the first or the second? What if an object in the XREF table has an incorrect offset? It is very easy to accidentally produce so-called file format schizophrenia: When the same file is rendered differently between two parsers. Be careful with PDF! There are many ambiguities in the specification that are implemented differently between parsers, as well as implicitly accepted malformations that almost all parsers will silently accept without warning.
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