I sometimes get asked to combine several PDF files into a single PDF file.

Here’s how I do it.

Combining PDF files on the terminal

List all PDF files (two, or more) then as the last argument specify the output file name (and remember to do this - you also won’t be warned if the output file already exists, it will just be overwritten).

pdfunite in-1.pdf in-2.pdf in-n.pdf out.pdf

“Considering that pdfunite is part of poppler it has a higher chance to be installed, usage is also simpler than pdftk.

IMPORTANT: Just make sure you remember to provide out.pdf, or else it will overwrite the last input file in your command”

Source: https://stackoverflow.com/questions/2507766/merge-convert-multiple-pdf-files-into-one-pdf

Combining PDF files in a web browser

Alternatively for a graphical tool, use:

https://www.stirlingpdf.com/

This can be self-hosted if required.