Scanned PDF files were also excluded since there is no sufficiently accurate Arabic Optical Character Recognition (OCR) system for the low resolution files we came across; although most of the OCRs available online claim high accuracy, tests reveal that their output needs editing (Abbas, Atwell and Al-Sulaiti 2016).
the 'Create Corpus' tool in SketchEngine (Kilgarriff et al 2014) enables researchers to gather texts in a range of different formats and then upload them into SketchEngine format.