PDF merge final check: inspect the joins

After merging PDFs, open the finished document and inspect every join between source files. Confirm that sections appear in reader order, no boundary page is duplicated or missing, and total page count equals the sum of inputs. Spot-check fonts, page sizes, links, bookmarks, and forms where needed. A successful download only proves a file was produced. The merged PDF should be readable at the transitions and should not unexpectedly expose pages from an unrelated source.