Thanks for the response - the envelope color and size (15 x 9cm) reminds me of the past. Is that an IBM Selectric?
Enclosed was a flyer from the 1980s by Istvan Kantor, which you can see more of on the Niels Lomholt Mailart Archive:
Also a bill for ONE ton of FLAX:
...and a note in response to a letter/flyer I sent earlier:
The letter that I sent, below:
Thank you, Miss Noma!