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Syncfusion provides .NET Core libraries to convert Excel (XLS, XLSX) and Word (DOC, DOCX) to PDF without the need of ...
The simplest solution is probably to use pdftotext from poppler-utils to extract the text, and then use an existing command line spell-checker (spell, ispell, aspell, etc...) to check it.
Note that if you are generating the PDF, you are probably better off checking the source of that generation, as words are liable to be bro- ken by being formatted in a PDF.
You could for example use Python 3:
with open(file_name) as file_to_check:
# read 8192 bytes of the file
data = file_to_check.read(8192)
# pipe contents of the file through
md5_returned = hashlib.md5(data).hexdigest()