Hi, Is there any size limit to send/receive document via web service

What method are you using to transfer the document? Some similar discussions can be found below:
forum.appian.com/.../e-140218
forum.appian.com/.../e-116810

For the base64 conversion, you are constrained to the amount of memory that is allocated for your Appian instance. If you were talking about using the HTTP File Upload/Download services, there is no mention of file size limits in the documentation but I would assume it would be similar since I believe it just encapsulates the Base64 conversion to avoid memory leak issues.

forum.appian.com/.../HTTP_File_Upload_Smart_Service.html
forum.appian.com/.../HTTP_File_Download_Smart_Service.html

Files of large sizes will cause an issue, it is better to write a custom plugin if your use case has large files

We had exposed webservice using servlet plugin (SOAP based using Axis 2 with MTOM) and dealt with few large files (most of them scanned pdfs 10MB or less , some of them as large as 100MB). It worked fine.