1. Forms available online for download: pdf, word and excel formats
CB Gallery can provide that functionality or you can use our download manager CB Package Builder (use custom types to avoid being used as Joomla installer).
2. Documents submitted online via the contact form: pdf, word and excel formats
We've no functionality for that. You'll likely need a custom form extension like RS Forms.
3. Generating invoices: pdf, word and excel formats
We've no functionality for that. Recommend using a Joomla extension specifically designed for generating invoices (there's a few on JED). The invoices generated by CBSubs are entirely automated and attached to a basket and are not available in PDF, word, or excel formats.
4. Receiving payments: PayPal, Debit Card, Credit Card
CBSubs can handle this, but it doesn't handle your invoice requirements above.