Create pdf form with bespoke page dimensions to fill and print

I am a Psychiatrist. I am looking to create a pdf (or if possible better Microsoft Word) document that will be blank and will contain a few areas to be completed such as patient's name and medication.
The reason why I am not able to do this on my own is that the prescription scripts I need to be able to populate have a size that is not A4 but rather a bit smaller than an A5.
The dimensions and the fields I require are in the attached image.
The document needs to be blank, with no text (perhaps a prefilled word such as NAME or DATE OF BIRTH to indicate which field you are in),
The most important part is that when I fill the form and print it it will print in the paper size that is 17.5 cm long x 10.5 cm wide which is the size of the script I need to feed to the printer in order to populate (I do not print the other fields of the script in the picture)
This should be a relatively easy job but I have no time to learn how to do it myself.