You're probably here because I've sent you an email reply asking if you could use a non-proprietary file format for your attachment(s). I would like to read what you say, but your chosen format makes this tricky as I don't have the software installed to open the file(s) you have sent me.
You've probably sent me a .docx, .xlsx or .pptx file from Microsoft Word, Excel or Publisher respectively. These are document formats that require proprietary software to open, unlike public document formats such as Plain Text (.txt), HTML (.htm or .html) or Adobe PDF (.pdf) files which can be opened with a number of free software applications. I'm generally unwilling to shell out money to Microsoft when there are perfectly good free alternatives available and as such, routinely can't avail myself of the contents of files created using their software. And when I can, I often find decoding issues such as incorrect fonts or images in the wrong place.
Please may I ask that you resend your attachments using a format that I can work with? Formats such as Plain Text, Markdown, HTML and PDF are ideal for written documents. Isolated images can be saved as PNG or SVG files whereas bulk data can usually be exported as a CSV file. If you wish to send me an archive or a directory/folder of files then a ZIP file is probably best. Thank you for your understanding!