PDF is the best format to save your resume. Saving your resume as a PDF ensures that the resume retains its formatting, is not able to be accidentally edited, and is easy for any hiring manager to open.
Some hiring managers will require you to submit a Word document when applying for a position. Generally, this is because they will use an applicant tracking system (ATS) to sort through their candidates for a particular position.
We recommend that you always submit a PDF unless the job ad specifically specifies for you to upload a Word doc. If you are unsure of the instruction, call the hiring manager to double check before you upload your submission.