1.  My job (Looking for someone who can improve my writting skills)

2.  For one year, I work at a pharmaceutical service provider as a Data Manager. It merely consists to build a database for a clinical trial. 3.  A clinical trial is a necessary step allowing a pharmaceutical laboratory to obtain a agreement for selling. They have to perform a  

4.  clinical trial for a health product like a drug of a medical device. The safety of the drug needs to be proven by the results of the clinical trial. Thus, the data management process is a part of whatever clinical research. During the research, I have to collaborate with a physician, statistician and a project manager.

5.  clinical trial for a health product like a drug of a medical device. The safety of the drug needs to be proven by the results of the clinical trial. Thus, the data management process is a part of whatever clinical research. During the research, I have to collaborate with a physician, statistician and a project manager.

6. trial. Thus, the data management process is a part of whatever clinical research. During the research, I have to collaborate with a physician, statistician and a project manager.

The numbers above make it easier to indicate corrections. 

1.  writing (not writting)
2.  Turn the sentence around and use the past tense: I worked as a data manager for a pharmaceutical service provider for one year.  
If you are still working in this position, use the present perfect tense and move "for one year" to the beginning of the sentence:

3.  ...is a necessary step FOR allowing....a SALES AGREEMENT. 
4.  ....for health productS, SUCH AS DRUGS OR MEDICAL DEVICES. Data .... is aN ESSENTIAL PART of clinical trials.