TNX ladies for your contributions. Always nice to know we are thinking about the same issues.
I think I will go for the presentation of the assignment in a pdf, and only in a pdf, and link to it in the introduction to the assignment. This way you prevent the double presentation which people may find confusing. A Word doc or a PPT slide that you save as a pdf is easier to format and students can take it where ever they want.
The pdf with instructions is for the goal of the assignment, criteria, tips for a good approach and what kind of feedback you receive. Students can open the pdf in another tab and switch easily from the instructions to the course page to look for reference to the topic they are working on and for resources.
I end the description field with: 'Are you content with the product you have made and are you confident you have met the criteria? Then click on Submit to send your work to me for feedback.'
At the end of the pdf one can provide a link to the assignment with a variation on this text.
The idea of making the reading of the assignment a condition for submitting it as a pretty logical one. However I deal mostly with adults and it feels a bit childish to do this.