How to count number of characters, words and sentences for page or selected text in Word document
Word counts the number of words, pages, paragraphs, lines, and characters (see How to see the number of characters, words and sentences in Word document). For example:

To calculate those numbers for a page or just some block of text, select it, and then do one of the following:
- On the Review tab, in the Proofing group, click Word Count:
or
- On the Status bar, click on the words count, for example:
Note: If you didn't see the words count of your document in the Status bar, right-click on the Status bar and select which data you want to see on it:
Word will open a Word Count dialog box with all counts for the selected text:

See also this tip in French: Comment compter le nombre de caractères, mots et phrases dans la page ou le texte sélectionné dans le document Word.