PDF merge before-and-after: compare sections, not file size

A merged PDF may be much smaller or larger than its inputs because objects are recompressed or duplicated. Review what matters: page sequence, page count, visible content, text extraction, links, bookmarks, and forms. Map each source section to its position in the output and inspect transitions. If a font or image changes appearance, compare that page in a second viewer. File size alone cannot establish that the merge preserved the document faithfully.