linux: added pdftk

wiki/linux/pdftk.md

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+# pdftk
+
+[pdftk](https://gitlab.com/pdftk-java/pdftk) is a port of
+[the original PDFtk](https://www.pdflabs.com/tools/pdftk-server/) which is a
+[command-line](/wiki/linux/shell.md) tool for scripting or processing PDFs.
+
+## Setup
+
+The pdftk program can be installed from source as described
+[on GitLab](https://gitlab.com/pdftk-java/pdftk).
+Alternatively many [Linux](/wiki/linux.md) [package managers](/wiki/linux/package_manager.md) 
+package pdftk in the `pdftk`.
+
+## Usage
+
+This section addresses the usage of pdftk.
+
+### Ommit pages at the Start or End of a PDF
+
+pdftk can be used to ommit pages at the start or end of a pdf.
+This is done by the following command.
+`<input-file>` is the input file while `<output-file>` is the path the newly generated file is
+saved to.
+`<start>` is the first page to include in the output PDF document while `<end>` is the last one.
+
+```sh 
+pdftk <input-file> cat <start>-<end> output <output-file>
+```
+
+The following command saves the content of the input file `skript.pdf` from the second to the last
+page to the output file `skript-new.pdf`.
+
+```sh 
+pdftk skript.pdf cat 2-end output skript-new.pdf
+```
+