Much of what I would suggest revolves around points of style rather than errors as such. On second thoughts, since when did clarity ever concern anybody involved in the churning out of business speak? How foolish of me.

2.3. Financial models construction, DCF;
You have a rogue 's' here; either 'Financial model construction' or 'Construction of financial models' will work. Indeed, how about 'formulation' instead of 'construction'?

2.4. Assistance in construction of deals and preparation documents for discussion;
Again, 'construction' sounds a bum note in English. 'The making of'? Or, for something flowery and gorgeous, 'orchestration'.

'...preparation of documents...'

2.5. Be responsible for clients’ files and documents, which are involved in work process.
'2.5. Responsibility for clients' files and [replace second clause with an appropriate adjective, eg. 'company'] documents.'

3.1. Assistance in preparation presentations for a client at the
selling stage;
'...preparation of...'

3.2. Preparation of an analytic conclusion for a project manager;
'Analytical' in this case. I'd also suggest a plural.

Generally speaking, your technical English is lovely.