sudo apt install qpdf

Remove a specific page using qpdf
qpdf input.pdf output.pdf --pages input.pdf <page-ranges> (1-5 6-7) --

Join / merge two PDFs using qpdf
qpdf --empty merged.pdf --pages file1.pdf file2.pdf --

Example: pages 1–3 from file1 + page 5 of file2:
qpdf --empty merged.pdf --pages file1.pdf 1-3 file2.pdf 5 --