You may need to share files between MacOS and Windows clients.   MacOS can usually open files from Windows computers.  And although a Windows PC can open a file saved by a Mac, there are two important requirements:
    1. The file must be saved in a common file format, so it can be opened by the software installed on either computer.
    2. The file name must be followed by a dot and a few letters (for example, .PDF or .DOCX).  This is called the file extension.
    When saving your work on a Macintosh, always use one of the file formats and extensions listed below. Mac programs like Keynote, Numbers, and Pages may not automatically save files in the correct format, but you can override those settings by doing a File > Save As.
     Type of File
     File Format  File Extension
     Word processing document
     Microsoft Word
     .doc or .docx
     Microsoft Excel
     .xls or .xlsx
     Slide presentation
     Microsoft PowerPoint
     .ppt or .pptx
     Photo or drawing
     Other  Adobe PDF  .pdf
    IMPORTANT: Some MacOS applications remove the file extension when you type a file name on the Save screen. Before sharing a file with someone, make sure it has a a file extension.  Windows PCs can't easily open a file with no extension after the name.