If you have your attachment on a piece of paper:
Follow these steps
- Scan it or take a picture of it. Make sure the entire document is visible and legible
- Save the file in pdf format
When you save the file in pdf format, it is important that it says '.pdf' in the lowercase file name. If '.pdf' does not appear at the end of the file, you should rename the file.
If you can not save the file in pdf format, convert it to pdf. There are many free online tools for this, such as for example Smallpdf.