Q: How can I put a document on my iPhone with Airdrop?

See this:  Use AirDrop to send content from your Mac - Apple Support

According to this document, you need an iPhone 5 or later: https://support.apple.com/en-us/HT204144.

Since you list an iPhone 6s and 2016 iMac,  your hardware are compatible with Airdrop .  Try restarting your router.

Hmm... for some reason I saw 4S. My mistake.

On both your iPhone and iMac, in AirDrop, what are they set to for "Allow me to be discovered by?"

Yes, that's exactly the issue.  From the article I posted:

• The iOS device must be using iOS 7 or later and have Personal Hotspot turned off in Settings > Cellular.

Are both Bluetooth and Wi-Fi on? Airdrop does not require a Wi-Fi network but Wi-Fi has to be turned on.

http://apple.stackexchange.com/questions/146644/airdrop-bluetooth-or-wifi

Are your restrictions set to Allow Airdrop? If so I would try emailing the document, not the same you asked but a workaround.

That's correct.  You need WiFi not supplied from your iPhone Hot Spot for Airdrop to work with your iMac.

You're welcome.  If this is a significant issue worth the cost, look into a Hotspot device from your carrier.