Thank you Alejandror,
I just tried your solution but after the second command I get:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'wkhtmltox' instead of './wkhtmltox_0.12.5-1.stretch_amd64.deb'
Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
wkhtmltox : Depends: libjpeg62-turbo but it is not installable
Depends: libssl1.1 but it is not installable
E: Unable to correct problems, you have held broken packages.