How duplicate pages happen
Feeding the same sheet twice through a scanner, merging two files that share pages, exporting a report twice into one file, or combining several versions of a document all leave repeated pages. They make documents longer, confusing and larger than necessary.
How duplicates are found
Each page is drawn at screen resolution and compared pixel by pixel with the other pages of the same size. Only pages that look exactly identical are treated as duplicates. The first time a page appears it is kept, and later copies are removed. The result note lists exactly which page numbers were removed. Up to 100 pages can be checked.
What counts as identical — and what does not
Two pages printed from the same digital file are usually identical and will be found. Two separate scans of the same paper almost never are, because tiny differences in position and lighting make the pixels differ — those pages are kept. Hidden text, links, form fields and metadata are not compared.
Common problems and how to fix them
A repeated scanned page was not removed: delete it manually with Delete PDF Pages. The PDF has more than 100 pages: split it with Split PDF, check each part, then merge them again. You want to remove blank pages instead: use Remove Blank Pages.
Good habits
Read the list of removed pages in the note, compare page counts before and after, and keep the original until you have checked the result.