> 1: *What's the main thing a paramedic does have to do?*  
 2: *What's the main thing a paramedic has to do?*

Example #1 above is *only* valid in contexts where the speaker is responding to having been told that a paramedic *doesn't* have to (isn't *required* to) do certain things - in which case ***does*** must always carry ***very heavy stress***.

Also note that the auxiliary ***have*** would almost always carry at least *secondary* stress, and be pronounced ***haff*** with a "hard" vowel ending rather than the soft vowel of ***have***. This is a special use of the verb form ***to have to [verb]*** (always followed by an infinitive verb), where it means ***be obliged to***. In Past Tense contexts it's usually pronounced ***hat*** rather than ***had***, so arguably it's actually a "different" verb, rather than a specialized sense of the existing verb.

---

Another way to illustrate the significant syntactic as well as semantic difference between the "obligatory" sense and the more general case is to consider...

> 3: *I don't have anything to do*  
 4:  *I don't have to do anything* (usually pronounced ***haff***)

...where #3 means *there are no (appealing) choices of action available to me* (effectively, *I'm bored*), whereas #4 means *there is nothing which I'm **obliged** to do*.

In the above examples, we can tell which sense is intended by the word order, but given a written utterance such as...

> 5: *These are the toys I have to play with*

...with no indication of stress or the pronunciation of the final vowel sound in ***have***, it's ambiguous whether the speaker means...

> 5a: *I **must** play with these toys*  
 OR  
 5b: *I have these toys **available to me** [if I wish to play with them]*