Hello @Estoy para ayudarlos,
I hope you are doing well, and thanks for reaching out. We're sorry for the trouble you had.
Could you please share more details about the issue? Are you on a Mac or Windows machine, and what is the version? Were the underlines added using Edit PDF, Comment/Annotate, or Fill & Sign tools?
Please enable the Automatically save document changes to temporary file every X minutes from the Menu > Preferences > Documents (Windows) or Acrobat > Preferences > Documents (macOS). Please note that Acrobat’s autosave creates a temporary backup file; it does not save directly to your PDF until you do a regular Save. When you close the PDF normally or manually save, Acrobat deletes the autosave backup.
What happens when you open the PDF file and go to Edit, or follow the same workflow? When you add underlines or other edits in Acrobat, always click the Save icon (or go to Menu > Save) periodically. This makes sure your changes (whether they’re comment annotations like underlines/highlights or actual content edits via Edit PDF) are immediately written to the file.
Please ensure you have the latest version of Acrobat installed on the machine: 26.001.21662. Planned update, Jun 09, 2026. Check for any pending updates by navigating to Menu > Help> Check for Updates. Install the updates, restart the app and the machine, and try again.
Let us know how it goes, and share your findings.
Regards,
Anand Sri.