Excel can be made to be beautiful, but I chose Word because my invoices are simple and I prefer to do my own calculations for same.
I'm not criticizing you, but you said, "simple software to generate invoices that I can save as PDFs and send." If the invoice is as simple as mine are I don't really need things to auto-calculate. I have billing sheets I submit that are Excel and do auto-calculate, but are not particularly pretty. They're really straight tables. I can genericize one of those if you'd like, but it would be a complex task to turn it into an invoice like you'd likely want.
I essentially wanted something that would be just like what I'd do with pen and paper on an old-style invoice pad, but generated on the computer, so that's what I did. You want something much more automated, it seems, and that's a different kettle of fish.
There are scads of free MS-Excel invoice templates that you can download and customize. See the results from this search: https://duckduckgo.com/?q=free+ms+excel+invoice+template&t=hq&atb=v33-7__&ia=web
This is how I've found the baselines for virtually anything I've used, but then customize the ones that come closest to what I was looking for.
This MS-Excel Invoice that calculates looks good as a starting point: https://templates.office.com/en-us/Service-invoice-TM00000031
Edited by britechguy, 13 July 2017 - 10:15 PM.
Added URL for specific Excel Invoice Template
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
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