What is exactly an FME mean and can it manipulate a document or how does it and manipulate the document

Your question is quite broad. Probably start at https://www.safe.com/fme/#how-it-works ?

Originally FME is an ETL (Extract Transform Load) tool, but in the current form it is a lot more than that.

Your Question is very generic

fme is Basically an ETL tool (Extract Transform and Load)

On the fly, you can manipulate / Generate/delete the data and write to Any format

it can read and write gis formats, raster formats, cad formats, or any attribute formats like MS excel to MS word or text file

you can do a lot of things, Whatever I say, It's just the tip of the iceberg

you can solve all your Line, point or polygon, island/ donut, or any geometry issues using fme.

Every Company should have this tool

A lot of work can be Automated using FME

More user-friendly, And it will be your good servant all the time.

I can say it is like a programming Language with visual functions

Using python (FME can call python programs within workbench / fmw file), you can Achieve any impossible

What to say, I'm not getting any words to express it. Thank Safe Canada for such a wonderful tool made.