Add all the PDF files you want to merge. The page order in the final file matches the order in which you added the files – drag them to reorder before processing.
Each file can contain any number of pages: they all appear in the merged PDF consecutively. There is no limit on the number of files – you can merge 2 documents or 30.
The result is a single PDF with no changes to formatting. If you need only specific pages from each file, split the source PDFs first, then merge the needed parts.