Long ago, I had to download data from ADP. Now, it's a different provider. Both had/have the same problem: no obvious way to export data to csv/ofx or anything other than pdf.
PDFs are a mess with automation. I use pdftotext, followed by a simple python parser/importer to get payroll data into Beancount. These days, I use
Tabula based on a
recommendation by Martin. The cool thing is, templates for pdfs can be saved and scripted. Now, things "just work" in automation 80% of the time once I go through the pain of downloading each paycheck separately.
I know you were looking for an ADP specific solution, but I thought I'd share my experience that it's not too much effort to cook up your own importer if you're unable to find an existing solution. Good luck!