You posted this in the Tax Talk section.

I assume you are the invited client of a tax preparer?

You seem to be sending photo files, but the tax preparation programs are a function as an office-type activity that is trying to manage documents. The other option available is the financial institution log in for tax-encoded documents (an industry standard in use for this function).

In other words, this is not a substitute for email or DropBox as storage, but a specific function.

I am sure you have the pdf output function. Example: "Step 2: Tap Print on the Share Sheet. On the Printer Options screen that shows up next, perform a Pinch Out (or Zoom In) gesture. The photo will be converted to the PDF format immediately. If you had multiple images selected, all items would be converted (and combined) automatically."

https://www.guidingtech.com/convert-photo-to-pdf-iphone-ipad/