Hi Almutasim,
Thank you for using Syncfusion products.
We have tried to reproduce the issue in the Blink converter, but it is working properly. We have created a simple sample with a basic bootstrap4 grid style in an HTML file, it generates the PDF document properly. The Bootstrap4 styles are rendered properly and we were not able to reproduce the issue. We have attached the sample and output document for your reference. Kindly please try the below sample in your end and let us know the result.
However, we are suggested you try the HTML string to PDF conversion in Blink converter. For this, we have to get the HTML string of your web page and then convert it to PDF document. Kindly refer to the below KB article and let us know if it is suites your requirement.
Please refer the below link for converting HTML string to PDF in Blink,
Note: When converting HTML string to PDF, we have to specify the base URL (path of the resources) to load the external images/scripts/styles used in the HTML string.
If still you are facing the same issue, kindly provide more details such as complete input HTML file/URL (with all resources styles, scripts, etc.,), product version to reproduce the issue in our end. So, that it will be helpful for us to analyze and assist you further on this.
Regards,
Gowthamraj K