Firefox can do basic annotating, adding text and adding pictures but it can’t make a new PDF from scratch.
You may be confusing Adobe Acrobat Reader with Adobe Acrobat? Full Acrobat is the proprietary tool to make a PDF file from scratch including some of the more complex functions.
PDF is an open standard and has been for a while, so there are now plenty of alternatives for most of the functions. LibreOffice Draw and Inkscape can do a lot of PDF creation functions but not all. There are also “print to PDF” options to create basic PDF documents too.
However some of the more niche functions are not widely supported or well supported; and there isn’t really any opensource dedicated PDF maker that I’m aware of. Layout tools are abundant but I think it’s things like building forms and document signing that is less easily replicated. There is Master PDF - a fully functional PDF maker which is proprietary and available for Linux; it $80 for a perpetual license. I’m not aware of any other alternatives myself.
They were talking about CO2 which is what the algae tank is about.
Trees have other benefits around filtering pollutants that affect air quality such as sulphur dioxide and nitrogen dioxide. Also the shading effect reduces ozone accumulation as well as generally helping reduce the urban heat island effect (which in turn reduces the amount of air conditioning needed, even a small amount saves energy and reduces pollution from power stations).
City parks have clean air partly because of tree but also because youre away from roads and buildings so further from car exhausts and chimney stacks. The concentration of pollutants in wide open spaces is lower because the wind can move it around more easily, and there isn’t a pollution source directly near by. Tree and grass do help too.
By far the most effective way of reducing pollution is reducing the sources. Trees are CO2 sinks and would reduce some CO2 if there was massive reforestation globally but that is outweighed by the ongoing CO2 production. The best solution is clean energy sources and getting rid of combustion engines.