Hi Alexandr,
Thank you for your interest in Syncfusion products.
We are not able to reproduce the mentioned issue ‘can't convert value to string’ error occurs while opening the word document using DocIO. For your reference we have attached the sample. Please do find the sample from the following link.
Sample Link:
Sample458972224.zipPlease do find the video illustration for the same from the below link.
Video Link:
video-1417122797.zipPlease let us know if you have any questions.
Regards,
Deiva Selvan