This free collection contains 12 different calendar icons.
If you are a Microsoft user the download link will get you a copy of these icons in PowerPoint, where you will be able to edit them (resize them and change their fill color, for example) from there, you can copy/paste them in Word or Excel or save them as PNG or SVG.
If you are a Google user, the link will let you make a copy of these icons in Google Slides, where you can customize them. You can copy / paste them in Drawings and export them to PNG (or SVG) and use the resulting clipart in Docs, Sheets or even Jamboard.
If you are not a Microsoft or Google user, you can choose to just download the PNG files. Just keep in mind that you won't be able customize them so easily.
For more information on how to edit and use these icons, please check out the how to section.