Maybe, maybe not.
All states using paper ballots put them through multiple phases of a scanning machine that first takes a picture of the signature and mark the ballot as received.
The second phase does an electronic comparison of the signature against the one on file - or other ones that exist from various sources.
The ballots are then read by machine, with the results stored in a way that election staff "cannot" get access until poll closing on election day.
Any ballots that have extraneous marks are then sent to a bipartisan team to determine voter intent, if possible.
Any signatures that cannot be verified are sent to people to manually check them - and to a bipartisan team if it still presents a problem.
There are a number of places along this "pretty good" pipeline where fraud can take place.
The ballot reader is a point of fraud. The single person verifying signatures that don't automatically match is a point of fraud. The votes being tallied prior to election day is a point of fraud if numbers can somehow be accessed.
As I said, the system if pretty good - but it's far from perfect - and this is in a state where they try to do a good job.
Bingo!
The weakest point for electronic subversion would be the tally software that counts the scanned ballots, or the database where the scanned ballots or precinct tallies are staged.
Malware introduced to compromise these items would almost certainly require an onsite agent to insert the applications. That might be possible to do some days before the activation, but the risk of detection or failure goes up considerably.
Once countermeasure would be to keep the tally systems air-gapped from internet connections (or any network connections), along with hourly check sums of all software and configuration files on those systems. Multiple backups of the staged scanned ballots and precinct tallies would catch data revisions, which could be audited for any anomalies.
Each batch introduced to the counting system would be logged and check summed.
Random selections of precinct tallies could be verified against counts in the main system, to catch other types of data manipulation.
They can have very low standards for what constitutes a match.