Is it legal to convert a png logo of a company you're partnering with and convert it to a SVG file for them to use it on an application we made? I am thinking there's a general license that forbids you from doing this. Do I have to send an email to all of them asking them to provide a SVG file, which would be tedious, or is it considered to be fair-use since the company is working with us to provide their API in our applications to our clients? Assume the company is in the United States.
Bringing fair use into this sounds iffy if you are partnering -- that is a commercial relationship which should be defined.
If they did send you a file with their logo for a specific purpose, you can assume that you are allowed to use it for that specific purpose. If they did not send you the file, you can assume that they did not give you permission, or they would have included the file ...
If you are partnering with them, you probably have implied consent to carry out acts within the foreseen scope of the partnership on their behalf.
It would be better to have a provision of the agreement in writing that says so, but it is hard to imagine them bringing a copyright infringement suit against a company they are working with that used the logo in connection with the joint enterprise without clearly prohibiting this conduct.