Combining PDF files?

[Scott Ehrlich]

If I have a collection of downloaded PDF files (someone else created
them), is a tool/method to combine them into one master pdf file?

The PDF files are not pieces to be recombined - they are
self-contained standalone files.  It would simply be convenient for me
to have them combined into one big file.

I may play with *nix's cat command, as I've used it to recombine files.

Thanks for leads and insights.

Scott