In the past I was using the tool pdftk in the command-line in my time when I was using Ubuntu and openSUSE.

With pdftk it is possible to merge pdf files to one pdf file. It was very useful for my job application.

With pdftk *.pdf cat output x.pdf

you can merge all your favoured pdf files in one folder to one file.

In the last year I had changed to Fedora and Fedora does not support the pdftk. I was desperately disappointed because pdftk was the main tool.

I have used pdf-shuffler. Pdf-shuffler is a graphical tool in order to merge pdf files. But I was not happy because you must click the pdf files to the program and etc.. It is very arduous for me. You cannot work quickly.

Now I have found pdf-stapler. It is only a command-line tool and today I was inquisitive to test how it works. I have found out that you can with:

pdf-stapler cat x.pdf y.pdf z.pdf

create a merged file. In my example is z.pdf the merged file.

you can also type in:

pdf-stapler cat *.pdf z.pdf

Now I have a new tool in order to merge pdf files. The program has not a manpage but with pdf-stapler -h you can see the syntax:

Usage: pdf-stapler [options] mode input.pdf … [output.pdf]

Modes:
cat/sel: <inputfile> [<pagerange>] … (output needed)
Select the given pages/ranges from input files.
No range means all pages.
del: <inputfile> [<pagerange>[<rotation>]] … (output needed)
Select all but the given pages/ranges from input files.
burst/split: <inputfile> … (no output needed)
Create one file per page in input pdf files (no output needed)
zip: <inputfile> [<pagerange>[<rotation>]] … (output needed)
Merge/Collate the given input files interleaved.
info: <inputfile> … (no output needed)
Display PDF metadata

Page ranges:
n – single numbers mean single pages (e.g., 15)
n-m – page ranges include the entire specified range (e.g. 1-6)
m-n – negative ranges sort pages backwards (e.g., 6-3)

Extended page range options:
…-end will be replaced with the last page in the file
R, L, or D will rotate the respective range +90, -90, or 180 degrees,
respectively. (e.g., 1-15R)