change string in MS word

[snippsat]

i didn't get something, then.
because when i try to use just python with a command like file.write(line.replace('this', 'that')) i have an error message

Open file as binary(rb) then there is no encoding problems.
You most look at doc or search how replace is done python-docx.
Quick test.

from docx import Document

file = open('Hello world.docx', 'rb')
document = Document(file)
for paragraph in document.paragraphs:
    if 'Hello' in paragraph.text:
        print(paragraph.text) # Hello world
        paragraph.text = paragraph.text.replace("Hello", "Ocean")

document.save('result.docx')

So now in result.docx it will say Ocean world