How could I attach a PDF file through my questions?
Excuse me for this question, but I have much trouble to do this!
Thank you very much.
Attaching pdf-files to posts is not supported.
You can only include an image. For details how to do this see How to upload an image to a post?
Of course, you can upload your pdf someplace on the internet and link to it.
However, please note that to the extent possible posts here should be self-contained, and including images should not be used as a quick-and-dirt substitute for typing up a question.