Love the product - In the plan is there the ability to combine PDFs - be willing to pay for this type of tool
While Sumatra is strictly a PDF reader only (which is what makes it so light and fast), there are a number free tools available to merge, split, renumber, etc. PDF files so you don’t have to pay for them. I personally use the tools from PdFill. They also have a very reasonably priced editor if you need to do more. Your mileage may vary.
No need to pay its already possible (but with limitations)
Any viewing program can use a virtual PDF printer that merges/combines files and there are many with powerful features to add coverpages or table of contents etc. but you would need to search for those.
SumatraPDF pre-release can combine separate PDFs with a combined virtual table of contents OR you can save the combined files currently without any table of contents, that’s the rub. (currently either / or)
Modify SumatraPDF settings to send 2 current tabs to an external command line tool such as that suggested by @Russ if that’s within your capabilities I can provide a template cmd file to gather two tabs filenames