Hi Manolo,
We regret for the inconvenience caused.
Please Ensure Syncfusion.pdf.base.dll assembly exists in the below mentioned location.
{Program files folder}\Syncfusion\Essential Studio\{Essential Studio version}\ precompiledassemblies\
Eg: C:\Program Files (x86)\Syncfusion\Essential Studio\16.1.0.32\precompiledassemblies\
If the Syncfusion.pdf.base.dll assembly exist the above mentioned location, you can refer directly to your project.
If still issue persist, follow the steps suggested in the kb article link and send us the zip file.
Regards,
Kalap Johnson Peter P.