How to merge PDF files in Linux

Merging PDFs in Ubuntu Linux or Linux Mint was real easy using the pdfunite command in a terminal. To merge PDF files in Linux open a terminal window enter the following command:
$ pdfunite file1.pdf file2.pdf file3.pdf combined.pdf <enter>

where file1.pdf, file2.pdf and file3.pdf are the individual pdf files that will be merged and combined.pdf is the merged pdf file.

To merge PDFs in Linux from a GUI interface, try PDFSam from