mjhjmtu

Is there any command which allows me to make some blocks of text invisible only if initially I said so?

I.e., I would like to mark some lines throughout the text that would only appear in the compiled pdf if in the beggining of the document I said something like: "those blocks of text ON"; and I don't want them to appear if I said something like "those blocks of text OFF".

The purpose of this is to generate two different documents: one with more deitailed information and another one without those details.

Note that this is not the same as the phantom or comment commands.

The simplest way would be to do something like this in the preamble:

newcommandadditionalInfo[1]#1

and then put all of those lines into that macro like this:

additionalInfoI am additional

If you don't want the lines to show up just replace above macro definition with

newcommandadditionalInfo[1]

Not as elegant as the other answers but in my opinion the simplest solution...

documentclassarticle

% switch comment to disable additional info
newcommandadditionalInfo[1]#1
% newcommandadditionalInfo[1]

begindocument
I am always here

additionalInfoI am additional
enddocument

One possibility is the multiaudience package:

documentclassarticle

% remove comment from the following line for the long version
%defCurrentAudiencelong



usepackagemultiaudience
SetNewAudiencelong
begindocument

normal text
beginshowntolong
 Text for execs
endshownto
normal text 

enddocument

You could use the ifthen package to implement this:

documentclassminimal

usepackageifthen
newbooleansomevariable
setbooleansomevariablefalse

begindocument

ifthenelsebooleansomevariableText if somevariable is true.Text if somevariable is false.

enddocument

I usually do this using new ifs:

documentclassarticle
newififprintsolution
printsolutiontrue
begindocument
Assignment.

ifprintsolution
Solution.
fi
enddocument

See e.g. https://www.bersling.com/2016/05/22/programming-in-latex/