A little known fact about Contact Form 7 is that you can dynamically set the values of your form input fields. Every Contact Form 7 input field supports the data-attribute. An advanced example on how to use this attribute can be found here: Dynamically populate a Contact Form 7 dropdown list (or any other input field)
The example above requires you to add a little bit of code to your theme, but there is also a much more straightforward way to set a value based on the querystring you add to your page URL with
default:get to all fields you would like to set dynamically, like this:
<label>Your name [text* your-name default:get]</label> <label>Your email [email* your-email default:get]</label> <label>Subject [text* your-subject default:get]</label> <label>Your message (optional) [textarea your-message default:get]</label> [submit "Submit"]
Now you can point people to this form with their information pre-filled in the URL, like this:
If you clicked the link above, you should now see that the fields in the form are pre-filled. You can also change the values in the URL and reload the page to see the fields update.