**4. Conclusions**

In total, the convertibility in enzymatic hydrolysis by a mixture of *P. verruculosum* B151 cellulase complex and F10 β-glucosidase of 69 samples of original and pretreated CCM was tested in this study. A major part of the non-pretreated substrates had a low convertibility of 3% to 18%. There were only a few substrates with a higher convertibility among the original unpretreated samples—e.g., soy bean husks had a convertibility of 31%, with sugar beat pulp at 20%. The low level of convertibility of CCM indicates the necessity of pretreatment [43,44].

Among the pretreated feedstocks, steam-exploded (with Ca(OH)2) soy bean and oat husks (76% and 58%), fine ball-milled aspen wood and nitric acid-pretreated aspen wood (62% and 78%), and steam-exploded (with sulfuric acid) corn stalks (55%) had a sufficiently high convertibility. It should be noted that types of cellulosic feed stocks that are the source of pulp and paper industry, such as newer dried kraft hardwood and softwood pulp (both bleached and unbleached), had a high convertibility (56–78%). This kind of CCM from our point of view had matching characteristics with the requirements for biomass enzymatic conversion to simple sugars and downstream processes, since they have a high convertibility, bulk availability, and waste disposal problems. The softwood and hardwood kraft pulp had a higher convertibility and are the most promising types of cellulose-containing materials from our point of view.

**Author Contributions:** Conceptualization, A.P.S.; Data curation, D.O.O. and G.S.D.; Formal analysis, D.O.O., G.S.D., and I.N.Z.; Investigation, D.O.O., G.S.D., E.G.K., I.A.S., and A.D.S.; Methodology, D.O.O., O.A.S., and I.N.Z.; Supervision, A.P.S.; Writing—original draft, D.O.O.; Writing—review and editing, A.P.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** The work was partially supported by the Russian Fund of Basic Research (#18-54-80027).

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analysis, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
