Fungi damage valuable documents mechanically, chemically and aesthetically because they form hyphae, excrete pigments and organic acids, generating particular local conditions that modify the physical-chemical properties of the different documentary supports. The aims of this research were to determine the fungal genera associated with the paper documents biodeterioration and to demonstrate the biofilm formation and the damages. Sampling was done from documents with signs of biodeterioration using sterile cotton swabs. After serial dilutions from the samples, plates with Extract Malt Agar were inoculated and incubated at 30 °C for 7 days. Additional little fragments of the damage zone from each analyzed document were observed using stereomicroscopy, environmental scanning electron microscopy (ESEM) and scanning electron microscopy (SEM). To evaluate the biodeterioration potential risk the strains were grown on cellulose, the acids production and pigments secretion were evaluated too. The genera Aspergillus, Cladosporium, Fusarium and Scopulariopsis were predominant. Isolated strains excreted acids into the culture medium; most of them grew well on cellulose and a few excreted pigments. The formation of a mature biofilm and the production of extracellular polymeric substances by fungi, as well as a dense biofouling mainly formed by dust mites, were evidenced by the SEM and ESEM observations. Also the observations showed that these strains were able to attach to paper fibre causing damage on them. The observation under optical microscopy of dead insect found inside the book showed fungal adhesion on the insect body and SEM support that this adhesion was formed by Aspergillus sp.