Create Adobe fillable form

Your most likely problem can be picked out frmo "they have Adobe on their computers". The user needs to understand how to fill PDF forms, or rather you need to explain it to them and support it. They need to know what software is which, so just saying "Adobe" suggests they may not have the right software. For example they might use "Adobe" to mean Adobe Flash Player or Adobe Photoshop. Adobe Acrobat Reader is what they need. Second, they need to actually USE it. This is not as trivial and obvious as it sounds. If you have Acrobat Reader on your computer but fill the form in your web browser or email app, then it (probably) won't be using Acrobat Reader. Your users need to be trained to download files and fill then using Reader. They also need to not just double click the downloaded file, it may run the wrong app. Users can find it hard to know what app is used.  And that's people with Mac and Windows. Well over half of people now use phones or tablets, and you need to support them too, and understand the important limitations.

All of this, in my personal opinion, diminishes the usefulness of PDF forms for a general audience. (Inside a company where you can mandate training and software, it's a different story). I suggest you look closely at HTML forms. There are many services. some free, which can allow forms to  be filled and returned to you via the web. Take care to consider the privacy of any personal info.

What app does they use? Adobe is a company with many apps.

In order to tell if there's a problem with the form, it would help if you could post a sample so we can test it out.