What does a checksum prove?

That two files are byte-for-byte identical. Nothing about authorship or date.

Should I send it with the file?

No. Record it separately. A checksum travelling with the document it describes can be regenerated by anyone who alters both.

Which algorithm should I use?

SHA-256 is the sensible default and is what most systems expect.

inspect

Compute a PDF Checksum

Compute a checksum so you can prove later that a file has not changed.

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How it works

A checksum is a short string derived from every byte of a file. Change anything at all and it changes completely, so anyone holding the same file can compute the same value and confirm nothing has been altered. It says nothing about who made the document or when — only whether it is the same one.

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Inspect PDF

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Questions

What does a checksum prove?: That two files are byte-for-byte identical. Nothing about authorship or date.
Should I send it with the file?: No. Record it separately. A checksum travelling with the document it describes can be regenerated by anyone who alters both.
Which algorithm should I use?: SHA-256 is the sensible default and is what most systems expect.