!pdftoolsパッケージでPDFファイルのテキストを読み込む

!!インストール

 install.packages('pdftools')
 library(pdftools)

で良いはずだが、インストール時にエラーが出る。

 Package poppler-cpp was not found in the pkg-config search path.
 Perhaps you should add the directory containing `poppler-cpp.pc'
 to the PKG_CONFIG_PATH environment variable
 No package 'poppler-cpp' found
 Using PKG_CFLAGS=-I/usr/include/poppler/cpp -I/usr/include/poppler
 Using PKG_LIBS=-lpoppler-cpp

素直に、エラーメッセージの指示に従う。↓

 ------------------------- ANTICONF ERROR ---------------------------
 Configuration failed because poppler-cpp was not found. Try installing:
 * deb: libpoppler-cpp-dev (Debian, Ubuntu, etc)
 * On Ubuntu 16.04 or 18.04 use this PPA:
    sudo add-apt-repository -y ppa:opencpu/poppler
    sudo apt-get update
    sudo sudo apt-get install -y libpoppler-cpp-dev