Compare Two PDFs

Every page of one document is compared with the page in the same position in the other, and the ones that differ are listed along with page counts, sizes and document properties. This is a way of finding where to look, not a description of what changed: a difference too small to see at comparison resolution — a digit, a date — may not register. For those, extract the text from both and compare that.

Will it catch a changed number?

Often, but not reliably. It compares how pages look. For small textual changes, compare the extracted text.

What if the documents are different lengths?

Only the overlapping pages are compared, and pages are matched by position rather than content.

Does it show me the difference?

It names the pages that differ. Look at those in your reader side by side.