If the toolkit Pdftk is available in the system, it will be called to manipulate the PDF files (especially to compress the PDF files).
pdftk(input, operation = NULL, output, other.opts = "compress dont_ask")the path of the input PDF file(s)
the operation to be done on the input (default to be
NULL)
the path of the output (if missing and input is a
scalar, output will be the same as input)
other options (default to be 'compress dont_ask',
i.e. compress the PDF files and do not ask the user for any input)
if ani.options('pdftk') is non-NULL, then this function
returns the status of the operation (0 for success; see
system); otherwise a warning will be issued
This is a wrapper to call pdftk. The path of pdftk should
be set via ani.options(pdftk = 'path/to/pdftk').
See the reference for detailed usage of pdftk.
Examples at https://yihui.org/animation/example/pdftk/
pdftk official website https://www.pdflabs.com/tools/pdftk-the-pdf-toolkit/