When I export to PDF the export fail and I get a blank page in the browser.

Please, check the all Vtiger parameters: https://it-solutions4you.com/tipstricks/vtiger-system-requirements/

You can also try performing the following steps:

1. Please download following zip file: http://its4you.sk/images/extensions/PDFMaker/src/mpdf.zip
2. Then go to the folder vtigerdirectory/modules/PDFMaker/resources.
3. Rename folder mpdf to mpdfOLD.
4. Open the zip file and copy mpdf from zip file to this folder.
5. Next go to the CRM, clear browser cache and try again.