I am planning to distribute an app with it's full functionality except that the number of objects the user can create within the app is restricted and on printouts a watermark will be shown.
The user can remove these restrictions at any time through an IAP purchases.
Will this violate any distribution rules or is that a viable way to allow the user a test-before-buy ?
Using IAP to sell expanded capability is common, I think. I also think the expectation is that the dev is able to balance what can be done for free with what needs to be paid for.
I'd avoid using the words eval & text & demo & trial etc. when completing that app's meta data, tho.
Keep in mind that App Review isn't here and there are no pre-reviews. You'll only find the opinions of other devs here.
See the ASRGs Section 3. Business
This is a common approach and on its face does not violate any guidelines. (Edit - except perhaps use of the term "Evaluation" as noted by another post - see Guidline 2.2 on Beta testing)
"...on printouts a watermark will be shown" - how about 1 printout with no watermark?
You will be well advised to write something either (or both) to the user's keychain on the device and to the user's key-value file in iCloud. That way if the user deletes and reinstalls the app the keychain will prevent them from getting a new set of free objects and if the user installs the app on a new device their iCloud key-value file will do the same.