He walked back, paid more than he wanted, and carted his prize to the historical-documents shop he owned in Lahaska.
Then he promptly forgot about the thing for the next 15 or so years. "I was never impressed with it," he says.
One day in 2006, Lingenfelter wondered if the Internet would yield any details about the curious phrase he saw printed on the bottom left of the paper:
Thus began a three-year treasure hunt, one that has cost Lingenfelter countless hours and a fair bit of money, and steeled his conviction that he has found a priceless piece of American history.
He says he owns a rare copy of the original Declaration of Independence, one made directly from the handwritten original by a long-forgotten transfer technique that is probably responsible for the original's deteriorated condition.
That would make his copy worth far more than replications of the typeset version of the Declaration of Independence, known as the Dunlap copy, one of which sold in 2000 for $8.14 million.
Or maybe not.
Taking another view is Karie Diethorn, chief curator of Independence National Historical Park, who says what Lingenfelter is banking on is an interesting theory, with no proof. She has her own theory.
"If I'm right," she says, "then there is nothing remotely remarkable other than it is an interesting use of a short-lived process."
Lingenfelter listens to her criticism, then goes to a shelf in his Doylestown home and pulls a swollen folder of documents he's been collecting.
He's not one to give up easily. You might recognize his name from his runs for public office - U.S. House of Representatives, most recently. He's a former Army intelligence officer, a sharpshooter, a white-haired man who, asked how one might describe him, replied: "I like the word curmudgeon."
His Web search led him to an Irish historian named Edward Law, who gave Lingenfelter a short course in the anastatic process.
In the 1840s, a Philadelphia printer and entrepreneur named John Jay Smith brought to this country a German-born and English-refined copying process that he hoped would make him a fortune.
The anastatic process made excellent copies with a catch - the wet transfer involved an acid wash that tended to ruin the original document.
For Lingenfelter's theory to be true, Smith would have had to have gained access to the document that was signed by most of the 56 delegates in Philadelphia on Aug. 2, 1776.
"There is no documentation to prove that," Diethorn says. "I don't see how Smith, who is just some guy, would have been given access in 1846 to the original Declaration of Independence."
More likely, she says, Smith copied a more common engraving made by William J. Stone.
In fact, she says, after Lingenfelter took his finding to Independence Hall, curators found a second anastatic replica in storage, one whose provenance they had been unsure of. So now there are two.
But, Lingenfelter replies, Smith wasn't just "some guy." He was the chief archivist for the Library Company of Philadelphia, which was the largest lending institution in the country at that time.
A researcher Lingenfelter has hired has found correspondence in which Smith and officials at the Library of Congress talked of going into business to copy a wealth of books, maps and documents.
Lingenfelter describes a scenario in which Smith quietly traveled to Washington and copied the original Declaration. "All that's missing," he says, "is my finding a note from Smith that says, 'Sorry, I [screwed up] the Declaration of Independence."
He makes one more point. His version and the Stone engraving - copies of which can sell for hundreds of thousands of dollars - have different spacings between the lines and are different sizes.
So what has he found?
Whatever it is, it looks a lot brighter these days. The Conservation Center in Philadelphia has removed the varnish coat, replaced a few frayed pieces.
Lingenfelter wants to take the document on a national tour so Americans can read the words that are so faded on the original.
Diethorn, while questioning the collector's theory, applauds his find and his success in uncovering a forgotten chapter in our nation's story. "This," she says, "is what the stuff of history is made of."
Contact Daniel Rubin at 215-854-5917 or firstname.lastname@example.org.