Open Adobe Acrobat
Ensure you are logged in to the Adobe programs (instructions HERE)
Go to Tools > Combine Files (the direct URL is https://acrobat.adobe.com/link/acrobat/combine-pdf/?group=group-edit)
Click Add Files and choose the documents you want to merge or drag and drop the files into the page
Arrange files by dragging them in order
Click Combine
Save the new document by clicking File > Save As
Finding the combined PDFs
To find your files, go to Adobe Acrobat and select the Documents tab (the direct URL is https://acrobat.adobe.com/link/documents/files/)