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It seems so. I can add the same arbitrary data at the end of two pdfs generated by this tool, and they are still a collision. I didn't know SHA-1 is so susceptible to length extension. Is there no internal state in the algorithm that would be different even if the hash output is identical?

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If you were to somehow get two messages with the same SHA-3 hash, you could keep on appending the same data to both and they would keep the same SHA-3. But SHA-3 is explicitly not vulnerable to length extension attacks.

No they wouldn't, since its internal state is different than the output.

Same goes for SHA-224 and SHA-384.

Damn, right, you have to get them with the same internal state.

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