Use Adobe Acrobat: Tools > Combine Files > Add Files > Combine
Use Preview on Mac: Open PDFs > View Thumbnails > Drag pages into order > File > Print > Save as PDF
Use PDFsam Basic: Open app > Merge > Add PDFs > Arrange order > Run
Use online PDF merger tools: Upload files > Arrange order > Merge > Download
Use Microsoft Print to PDF on Windows: Open each PDF > Print to PDF or use a merge tool first
Use command line with Ghostscript: `gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=merged.pdf file1.pdf file2.pdf`
Use command line with pdftk: `pdftk file1.pdf file2.pdf cat output merged.pdf`
Use command line with qpdf: `qpdf –empty –pages file1.pdf file2.pdf — merged.pdf`
Use Python with PyPDF2 or pypdf: read files > append pages > write output PDF