Drag the list to set the order - page 1 of the first file, then the next, and so on
Click Merge and download the combined document
Splitting PDFs
Use Extract PDF Pages to pull specific pages into a new file (handy for sending just one page of a contract), or Split PDF to break a document into parts.
Common combinations
Scanned pages + an existing PDF: scan with the phone scanner, generate the PDF, then merge it with the other file
Large merged result too big? Compress PDF afterwards