What version of Forms are you using? Does it work if you store the submitted forms as Tiff instead of Pdf or does saving as Tiff experience the same issue?

If you create a new Forms with few controls, does it also experience the same issue? (basically narrow down if there are other factors that might be contributing to the issue, such js, css, etc..). 

Forms uses to create the PDFs a third party component. You can try uninstalling this component  "wkhtmltopdf" application from the Windows Control Panel (Programs and Features). Then manually browse the Forms 10/9.2 installation package and reinstall that component.

Additional Recommendations:

Ensure you have the latest updated installed for the version that is applicable to you. Forms 9.2.1 , ensure update 1 is installed on KB 1013728, For Forms 10 KB 1013725

I do recommend to contact your reseller to open a case with Laserfiche Tech Support to do further troubleshooting, Please make sure the case contain the following information.:

1. Copy of the exported business process - xml format

2. Exact version and build number of the Form server.

3. In case this is laserfiche forms version 9.x , a copy of the application and system event logs in evtx format are required to review errors that are taking place in the background.  If the Forms server version is 10 , provide a copy of LFForms event logs, to be found in Event Viewer under section "Application and Services Logs".