Always send your resume in PDF.
There are a few reasons why this is better than Word:
Nobody can edit it. Let’s say someone’s got your CV open on their computer. They get a quick phone call and type something into your resume… Now that’s a typo which will unnecessarily reflect on you.
Not all computers have MS Word. If they don’t have MS Word, they might not be able to open your file. And they might not go to the trouble of converting your resume into a compatible format.
Your fonts might not be available on their end. If the receiver of your CV doesn’t have the fonts in your file, it might render very differently and look a little messed up. Even if the hiring manager has the fonts, if it gets forwarded through a recruiter or middleperson who doesn’t, the fonts will still be lost.
PDFs are easier to open on mobile. A lot of hiring managers take a first look at incoming resumes on their smartphones. You want them to be able to access your CV from their preferred device.
So, send a PDF version of your resume. PDF embeds fonts, which will render similarly on others’ screens and is infinitely better than the editable Word. I know you’ve put a lot of effort into designing your CV — you want it to look good on their computers as well!