Building a Form - Need to add a field for adding an Attachment or Upload with every submission.

Yes, this is built into Airtable, so you can do this natively with Airtable's built-in forms. Simply add an attachment field to your form.

For even more advanced usage of attachment fields on forms, you can turn to Fillout’s advanced forms for Airtable.

Fillout is 100% free and offers hundreds of features that Airtable’s native forms don’t offer, including the ability to update Airtable records from a form, display Airtable lookup fields & Airtable rollup fields & Airtable attachments & formulas on forms, upload unlimited attachments simultaneously (and optionally put limits on those attachments by size, quantity, or attachment type), dynamically & conditionally filter linked record fields by any values that you would like, perform math or other live calculations on your forms, accept payments on forms, create multi-page forms with conditional paths, create new linked records on a form, display as many fields as you want to see in a linked record selection list (including attachments), and so much more. 

Hope this helps! If you’d like to hire an expert Airtable consultant to help you with anything Airtable-related, please feel free to contact me through my website: Airtable consultant — ScottWorld

In addition to what ScottWorld has posted, Plumsail Public Forms can be a great option for you. They're user-friendly, highly customizable, and allow file uploads— including images, PDFs, and other documents— which automatically get stored in your table. Plumsail also offers a free account for public forms.