Use a temporary directory:
require 'docsplit'
def pdf_to_text(pdf_filename)
Docsplit.extract_text([pdf_filename], ocr: false, output: Dir.tmpdir)
txt_file = File.basename(pdf_filename, File.extname(pdf_filename)) + '.txt'
txt_filename = Dir.tmpdir + '/' + txt_file
extracted_text = File.read(txt_filename)
File.delete(txt_filename)
extracted_text
end
pdf_to_text('doc.pdf')