Make a Multiple Page PDF

In Apple Preview

1. Open your first PDF in Preview.
2. Go to 'Edit > Insert > Page from File…'.
3. Select your additional PDFs from the dialog and click 'Open'.
4. Go to 'File > Save' to save the changes to the PDF.

In Adobe Acrobat

1. Open your first PDF in Acrobat.
2. On the right hand side select 'Combine Files' from the tools list. If you cannot see this go to 'View > Tools > Combine Files > Open'.
3. Click 'Add Files'.
4. Select your additional PDFs from the dialog and click 'Add Files'.
5. Click 'Combine' on the top right hand side.
6. Go to 'File > Save As…' and save your new PDF.