Pdftk

Appending multiple pdfs with pdftk:

 pdftk file1.pdf file2.pdf file3.pdf cat output newfile.pdf

Yes! yOu can Append multiple pdfs with a wildcard with pdftk:

 pdftk *.pdf cat output newfile.pdf

https://www.maketecheasier.com/combine-multiple-pdf-files-with-pdftk/