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I just tried it on a bank statement and the only text I see is the PDF commands (stuff like "/MediaBox [0 0 612 792]", "/F1 125 Tf", and whatnot). There's no ac

I just tried it on a bank statement and the only text I see is the PDF commands (stuff like "/MediaBox [0 0 612 792]", "/F1 125 Tf", and whatnot). There's no actual PDF content text that I can find, whether it's my name, the bank name, or anything else.

mkl 8y ago
There are a few possibilities. The main PDF commands for text are "Tj" and "TJ", so you can try searching for them. Text commands must also be between "BT" and "ET". Maybe a bit harder to search for are the other two text commands: ' and ". TJ is "Show text, allowing individual glyph positioning" which means strings are not necessarily in the PDF as the strings themselves, but have glyph positioning info mixed into them. This is the most common issue I've come across. Another possibility is that the fonts have been combined/compressed/butchered, so that they're not using ASCII/Unicode (this can sometimes save space by combining bits of multiple fonts. Searching for Tj/TJ/'/" should tell you if that's the case. If it is, technically there should be a translation table somewhere in the PDF file (so that clipboard operations work in PDF viewers). Look for CustomEncoding, I think. Particularly bad PDF creation libraries can put characters in one by one. Characters (alone or in strings) can also be in there as octal or hex. Finally, particularly obnoxious libraries can do it without text commands at all, but convert everything to vector drawing commands, or even worse, bitmaps. I couldn't remember CustomEncoding, and this came up when I searched. Seems helpful: https://stackoverflow.com/questions/29467539/encoding-of-pdf-text-string https://stackoverflow.com/questions/29467539/encoding-of-pdf...
- mehrdadn 8y ago
  Interesting, thank you for the explanation! I am indeed seeing a lot of Tj's and BT/ET's, but not any TJ's. Immediately preceding the Tj's are a lot of non-text characters that don't look like anything human-readable. Immediately following them are other other commands (Td, Tf, rg, k, etc.) which are preceded by numbers. There are no CustomEncodings. So I guess this means I can't really grep anything?
  - mkl 8y ago
    Sounds like it. The T commands are text related and rg and k are setting colour in RGB and CMYK. You may be able to figure it out by changing a colour, then looking at what is suddenly bright red or whatever you set. Or by changing the string preceding Tj. When editing, make sure you don't change the length of any objects (use space to pad) as there are hardcoded offsets in a table, usually at the end. The PDF specification, while long, is pretty readable for this kind of thing. You can download the 1.7 version free from Adobe. Appendix A has a table of commands.
    - mehrdadn 8y ago
      Thanks! This was cool info.

mkl 8y ago

There are a few possibilities. The main PDF commands for text are "Tj" and "TJ", so you can try searching for them. Text commands must also be between "BT" and "ET". Maybe a bit harder to search for are the other two text commands: ' and ". TJ is "Show text, allowing individual glyph positioning" which means strings are not necessarily in the PDF as the strings themselves, but have glyph positioning info mixed into them. This is the most common issue I've come across. Another possibility is that the fonts have been combined/compressed/butchered, so that they're not using ASCII/Unicode (this can sometimes save space by combining bits of multiple fonts. Searching for Tj/TJ/'/" should tell you if that's the case. If it is, technically there should be a translation table somewhere in the PDF file (so that clipboard operations work in PDF viewers). Look for CustomEncoding, I think. Particularly bad PDF creation libraries can put characters in one by one. Characters (alone or in strings) can also be in there as octal or hex. Finally, particularly obnoxious libraries can do it without text commands at all, but convert everything to vector drawing commands, or even worse, bitmaps. I couldn't remember CustomEncoding, and this came up when I searched. Seems helpful: https://stackoverflow.com/questions/29467539/encoding-of-pdf-text-string https://stackoverflow.com/questions/29467539/encoding-of-pdf...

mehrdadn 8y ago
Interesting, thank you for the explanation! I am indeed seeing a lot of Tj's and BT/ET's, but not any TJ's. Immediately preceding the Tj's are a lot of non-text characters that don't look like anything human-readable. Immediately following them are other other commands (Td, Tf, rg, k, etc.) which are preceded by numbers. There are no CustomEncodings. So I guess this means I can't really grep anything?
- mkl 8y ago
  Sounds like it. The T commands are text related and rg and k are setting colour in RGB and CMYK. You may be able to figure it out by changing a colour, then looking at what is suddenly bright red or whatever you set. Or by changing the string preceding Tj. When editing, make sure you don't change the length of any objects (use space to pad) as there are hardcoded offsets in a table, usually at the end. The PDF specification, while long, is pretty readable for this kind of thing. You can download the 1.7 version free from Adobe. Appendix A has a table of commands.
  - mehrdadn 8y ago
    Thanks! This was cool info.