You may experience issues when viewing a PDF file containing thin lines. Thin lines may disappear at different zoom levels. The thin line display issue can occur with PDF files created from any vendor. This is because the appearance of table lines is affected by the limited resolution of the display monitor. If you print a hard copy of the same PDF file, then the lines will appear correctly because the resolution of the printed page is higher than that of the display monitor.
Designing your forms with thicker lines may help prevent this issue.
You may also consider changing Adobe Acrobat Reader's default behavior to enhance the display of thin lines on the display monitor. This behavior can be changed by going to Edit, Preferences, Page Display, then check/uncheck 'Enhance Thin Lines'.
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